Urban Wastewater Treatment Using Vermi-biofiltration System

9
Urban wastewater treatment using vermi-bioltration system Priyanka Tomar, Surindra Suthar School of Environment & Natural Resources, Doon University, Dehradun-248001, India abstract article info Article history: Received 3 June 2011 Received in revised form 8 September 2011 Accepted 9 September 2011 Available online 13 October 2011 Keywords: Wastewater treatment Perionyx sansibaricus COD TDS Vermi-bioltration Marshy plants This work illustrates the potential of a novel vermi-bioltration system in treatment of urban wastewater. A small-scale vermi-bioltration reactor was constructed using vertical subsurface-ow constructed wetlands (VSFCWs) aided with local earthworms Perionyx sansibaricus. The coco-grass: Cyprus rotundus (density 0.14 plants/in. 2 ) was used to construct VSFCW. Another reactor without earthworms acted as experimental con- trol. The wastewater was treated through this system for a total of eight repetitive cycles and after each cycle the changes in pH, electrical conductivity (EC), total dissolved solids (TDS), and total suspended solids (TSS), chemical oxygen demand (COD), NO 3 - and PO 4 3- of water were measured. Vermi-bioltration caused signif- icant decrease in level of TSS (88.6%), TDS (99.8%), COD (90%), NO 3 - (92.7%) and PO 4 3- (98.3%). There were about 38.8, 20.8, 80.6, 50.8 and 144.6% more removal of TSS, TDS, NO 3 - , PO 4 3- and COD, respectively in vermi-bioltration than control. Results thus suggested that vermin-bioltration system is more efcient than VSFCW in terms of contamination removal efcacy. However, this work provides a preliminary idea of using earthworms in wastewater treatment system and further detailed studies are required on some key issues (e.g., loading rate, ow alternation impacts and earthworm stocking density) of this system. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The urban runoff in general, carries organic load along with sever- al hazardous chemicals which not only spoils the aesthetic sense of the river but at the same time also degrades the aquatic ecosystem. Due to high establishment and running cost of a sewage treatment plant (STP) the majority of urban centers in developing world dispose urban runoff and sewerage water directly into urban river without any treatments or with partial treatments. Several mechanical and chemical approaches are being applied widely for urban wastewater treatments systems in urban centers mainly by sewage treatment plants (STPs). Apart to construction costs the operation and mainte- nance problems in STPs has raised the question of sustainability [1]. Moreover, excess sewage sludge produced by STPs has been sub- jected to increasingly stringent limitations on discharge during the last few decades [2]. According to Sinha et al. [3] many developing countries cannot afford the construction of STP and therefore; there is growing concern over developing some ecologically safe and eco- nomically viable small-scale wastewater treatment technologies for onsite wastewater treatment. However, at this crucial juncture some ecologically engineered tools can solve issues related with safe and cost-effective wastewater treatments technologies. The majority of present wastewater treatment systems are a disposal-based liner systemand they should be transformed into cyclical treatments [4] in order to conserve the water and nutrient resources. An economical and manageable wastewater treatment approach is often required and deserves to be explored [5]. Biological wastewater treatment process involves the potentials of some living organisms to remove contaminants and sludge from wastewater in order to make it suitable for surface irrigation and other industrial use. Biological wastewater treatment involves the transformation of dissolved and suspended organic contaminants to biomass and evolved gases: CO 2 , CH 4 ,N 2 and SO 2 [6]. A variety of or- ganism like aquatic plants, marshland plants, protozoa, nematodes, oligochaetes have been tested in both laboratory and eld conditions to develop a low-cost bioreactor for wastewater treatment and sludge reduction. The potential of oligochaetes for wastewater treatment and sludge has been explored widely in many parts of the world. In general, Oligochaetes can be divided into two distinct groups, rstly, microdrilli (aquatic and small sized worms) and, secondly, terrestrial oligochaetes (earthworms) [7]. The aquatic oligochaetes can be divid- ed into two groups: (i) the large aquatic worms (Tubicidae, Lumbri- culidae and the semi-aquatic or terrestrial Enchytraeidae) and, (ii) the small aquatic worms such as Naidids and Aeolosomatids [8]. In recent years, both aquatic and terrestrial oligochaetes have been tested by several authors under lab-based trials to remove water contaminants and excess quantity of sludge [3, 6, 8-13]. The major components and outcomes of previous experiments on vermi-bioltration are de- scribed in Table 1. The utilization of earthworms in wastewater or sludge treatment is called vermi-bioltration. It was rst advocated by the Prof. Jose Toha at the University of Chile in 1992 [22]. Vermi-bioltration is a Desalination 282 (2011) 95103 Corresponding author. Tel.: + 91 135 2255103. E-mail address: [email protected] (S. Suthar). 0011-9164/$ see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.09.007 Contents lists available at SciVerse ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal

Transcript of Urban Wastewater Treatment Using Vermi-biofiltration System

Page 1: Urban Wastewater Treatment Using Vermi-biofiltration System

Desalination 282 (2011) 95–103

Contents lists available at SciVerse ScienceDirect

Desalination

j ourna l homepage: www.e lsev ie r .com/ locate /desa l

Urban wastewater treatment using vermi-biofiltration system

Priyanka Tomar, Surindra Suthar ⁎School of Environment & Natural Resources, Doon University, Dehradun-248001, India

⁎ Corresponding author. Tel.: +91 135 2255103.E-mail address: [email protected] (S. Suthar).

0011-9164/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.desal.2011.09.007

a b s t r a c t

a r t i c l e i n f o

Article history:Received 3 June 2011Received in revised form 8 September 2011Accepted 9 September 2011Available online 13 October 2011

Keywords:Wastewater treatmentPerionyx sansibaricusCODTDSVermi-biofiltrationMarshy plants

This work illustrates the potential of a novel vermi-biofiltration system in treatment of urban wastewater. Asmall-scale vermi-biofiltration reactor was constructed using vertical subsurface-flow constructed wetlands(VSFCWs) aided with local earthworms Perionyx sansibaricus. The coco-grass: Cyprus rotundus (density 0.14plants/in.2) was used to construct VSFCW. Another reactor without earthworms acted as experimental con-trol. The wastewater was treated through this system for a total of eight repetitive cycles and after each cyclethe changes in pH, electrical conductivity (EC), total dissolved solids (TDS), and total suspended solids (TSS),chemical oxygen demand (COD), NO3

− and PO43− of water were measured. Vermi-biofiltration caused signif-

icant decrease in level of TSS (88.6%), TDS (99.8%), COD (90%), NO3− (92.7%) and PO4

3− (98.3%). There wereabout 38.8, 20.8, 80.6, 50.8 and 144.6% more removal of TSS, TDS, NO3

−, PO43− and COD, respectively in

vermi-biofiltration than control. Results thus suggested that vermin-biofiltration system is more efficientthan VSFCW in terms of contamination removal efficacy. However, this work provides a preliminary idea ofusing earthworms inwastewater treatment system and further detailed studies are required on some key issues(e.g., loading rate, flow alternation impacts and earthworm stocking density) of this system.

rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

The urban runoff in general, carries organic load along with sever-al hazardous chemicals which not only spoils the aesthetic sense ofthe river but at the same time also degrades the aquatic ecosystem.Due to high establishment and running cost of a sewage treatmentplant (STP) the majority of urban centers in developing world disposeurban runoff and sewerage water directly into urban river withoutany treatments or with partial treatments. Several mechanical andchemical approaches are being applied widely for urban wastewatertreatments systems in urban centers mainly by sewage treatmentplants (STPs). Apart to construction costs the operation and mainte-nance problems in STPs has raised the question of sustainability [1].Moreover, excess sewage sludge produced by STPs has been sub-jected to increasingly stringent limitations on discharge during thelast few decades [2]. According to Sinha et al. [3] many developingcountries cannot afford the construction of STP and therefore; thereis growing concern over developing some ecologically safe and eco-nomically viable small-scale wastewater treatment technologies foronsite wastewater treatment. However, at this crucial juncture someecologically engineered tools can solve issues related with safe andcost-effective wastewater treatments technologies. The majority ofpresent wastewater treatment systems are a “disposal-based linersystem” and they should be transformed into cyclical treatments [4]

in order to conserve the water and nutrient resources. An economicaland manageable wastewater treatment approach is often requiredand deserves to be explored [5].

Biological wastewater treatment process involves the potentials ofsome living organisms to remove contaminants and sludge fromwastewater in order to make it suitable for surface irrigation andother industrial use. Biological wastewater treatment involves thetransformation of dissolved and suspended organic contaminants tobiomass and evolved gases: CO2, CH4, N2 and SO2 [6]. A variety of or-ganism like aquatic plants, marshland plants, protozoa, nematodes,oligochaetes have been tested in both laboratory and field conditionsto develop a low-cost bioreactor for wastewater treatment and sludgereduction. The potential of oligochaetes for wastewater treatmentand sludge has been explored widely in many parts of the world. Ingeneral, Oligochaetes can be divided into two distinct groups, firstly,microdrilli (aquatic and small sized worms) and, secondly, terrestrialoligochaetes (earthworms) [7]. The aquatic oligochaetes can be divid-ed into two groups: (i) the large aquatic worms (Tubificidae, Lumbri-culidae and the semi-aquatic or terrestrial Enchytraeidae) and, (ii) thesmall aquatic worms such as Naidids and Aeolosomatids [8]. In recentyears, both aquatic and terrestrial oligochaetes have been tested byseveral authors under lab-based trials to remove water contaminantsand excess quantity of sludge [3, 6, 8-13]. The major components andoutcomes of previous experiments on vermi-biofiltration are de-scribed in Table 1.

The utilization of earthworms in wastewater or sludge treatmentis called vermi-biofiltration. It was first advocated by the Prof. JoseToha at the University of Chile in 1992 [22]. Vermi-biofiltration is a

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Table 1Earlier studies indicating potential of oligochaetes in sludge stabilization and wastewater treatment.

Type of sludge/wastewater Worm species used Major observations References

Aquatic worm ((Tubificidae, Lumbriculidae, Naidids and Aeolosomatids)Waste sludge produced in wastewatertreatment plant

Lumbriculus variegatus Sludge reduction was 77% duringthe process

Hendrickx et al. [11]

Waste sludge produced in wastewatertreatment plant

Lumbriculus variegatus TSS reduced up to 99% aftertreatment

Elissen et al. [14]

Effluent of activated sludge process Lumbriculida hoffmeisteri Worm effectively removes majorpollutant from sludge

Wei et al. [15]

Sludge from wastewater water Branchnria Sowerbyi, Limnodrilns There was drastic impact on sludge(46.4% reduction in first stage),COD (more than 80% removal) andBOD (more than 81%) during the process

Song et al. [16]

Sewage of domestic sludge Lumbriculus variegatus 20–40% sludge converted into wormbiomass and nitrate as well as nitriteremoved efficiently

Buys et al. [17]

EarthwormsDomestic wastewater (assessment of toxicity ofammonia on earthworm in vermi-biofiltration system)

Eisenia fetida High salt concentration may causedamage to earthworms in vermifltrationunits

Hughes et al. [10]

Liquid waste products from dairy industry E. fetida Removal of 5 day BOD by 98%,COD by 80–90%, TDS by 90–92%during the process

Sinha et al. [3]

Domestic wastewater sludge E. fetida Significant reduction in pollutantduring vermistabilization process

Wang et al. [5]

Secondary liquid effluents from Gelatine Industry Lumbricus rubellus Decrease in COD by 90% and BODby 89%.

Ghatnekar et al. [18]

Raw sewage E. fetida, Perionyx excavatus,Eudrilus euginae

Removal of COD by 80–90% andBOD by 90% during vermi-biofiltration

Sinha et al. [19]

Treatment of sewerage and sludge E. fetida Removal of COD by 81–86% andBOD by 90–98% during vermi-biofiltration

Xing et al. [20]

Domestic wastewater treatment E. fetida Removal of COD by 55–66% andBOD by 47–65% during process

Xing et al. [21]

96 P. Tomar, S. Suthar / Desalination 282 (2011) 95–103

process that adapts traditional vermicomposting system into a pas-sive wastewater treatment process by using potentials of epigeicearthworms. According to Komarowski [23] in vermi-biofiltrationsystem suspended solids are trapped on top of the vermifilter andprocessed by the earthworms and fed to the soil microbes immobi-lized in the vermifilter. The dissolved and suspended organic and in-organic solids are trapped by adsorption and stabilization throughcomplex biodegradation processes that take place in the “living soil”inhabited by earthworm and the aerobic microbes. Intensification ofsoil processes and aeration by earthworms enable the soil stabiliza-tion and filtration system become effective and smaller in size [19].In general, inoculated earthworms in vermibeds accumulate many or-ganic pollutants from the surrounding soil environment, passive absorp-tion through the bodywall and also intestinal uptake during the passageof soil through the gut [24]. The efficacy of vermi-biofiltration system isalready described in literature (Table 1). Sinha andhis group investigatedthe potential of vermi-biofiltration system in treatment of dairy industryeffluent [3]. They claimed that earthworms have been found to removethe 5 day BOD by over 98%, COD by 80–90%, TDS by 90–92% from anyliquid wastes by the general mechanism of ingestion and biodegrada-tion of organic wastes. According to a study conducted by Ghatnekaret al. [18] suggested that the vermi-biofiltration system is efficient to re-move COD and BOD load of wastewater generated from gelatin indus-try. They applied a three-tier biotechnology unit coupled with vermi-biofiltration system to convert secondary liquid effluents from a gelatinmanufacturing unit into bio-safe clean water. Results thus, suggested asignificant decrease in COD by 90% and BOD by 89%. Recently, Zhao et al.[2] studied the stabilization of domestic waste water sludge usingearthworms and results have revealed that the presence of earthwormsin the vermibeds to the significant stabilization of the sludge. The vola-tile suspended solids (VSS) reduction in the vermibeds was in theranges of 56.2–66.6% in different treatment units aided with earth-worms. Similarly, Sinha et al. [19] developed a low-cost sustainable

technology over conventional systems to recycle the domestic waste-water with potential for decentralization facility for waste manage-ment. They claimed removal of 5 days' BOD (BOD5) by over 90%, CODby 80–90%, total dissolved solids (TDS) by 90–92%, and the total sus-pended solids (TSS) by 90–95% from urban wastewater after the treat-ment with worms. The microbes play an important role in vermi-biofiltration system and they also provide some extracellular enzymesto facilitate the earthworms for rapid degradation of organic substancesin vermibeds [25]. Likewise, Zhao et al. [2] investigated the interactionsbetween microorganism and earthworm in vermi-biofiltration system.They demonstrated that earthworm biofilm was dominated by themembers of the phylum Proteobacteria and Pseudomonas sp.

The majority of previous studies are available on either utilizationof vermi-biofiltration or only constructed wetland filtration systemfor removal of nutrients/pollutants from wastewaters, but no com-prehensive report is available on utilizing potentials of both systemsto develop an effective integrated system, comprising of earthwormand construction wetland system, for wastewater treatment. Al-though, Chiarawatchai [26] has conducted an interesting study oncombining vertical sub-surface flow constructed wetlands (VSFCWs)with earthworm. The integration of these two ecological techniques(traditional wetlands system with vermi-biofiltration mechanism)can be a cost effective and sustainable option for onsite wastewatertreatment.

The aim of this study was to assess the potential of an integratedvermi-biofiltration system with VSFCWs constructed by using earth-worm Perionyx sansibaricus and a wetland weed Cyprus rotundus(coco-grass or red nut sedge) under a small-scale laboratory experiment.C. rotundus is one of the most invasive weeds and have been reportedfrom tropical and temperate regions of the world. It is a perennialplant and mainly occurs in gardens, agriculture plots, around stagnatewater bodies etc. Few earlier studies have demonstrated the capabilitiesof C. rotundus in wastewater treatment and phytoremediation [27–29].

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C. rotunduswas selected for vermi-biofiltration system due its local andperennial availability, short length (up to 40 cm) and easy cultivationcapabilities.

2. Materials and methods

2.1. Earthworm, plant collection and wastewater collection

Individuals of earthworm Perionyx sansibaricus of different age groupwere collected from mud of a gray water drain in university campus,Dehradun, India. The stock of P. sansibaricus was cultured in laboratoryusing garden soil spiked with leaf litter and cow dung inappropriate ra-tios. Plant Cyprus rotundus used for construction of biofiltration unitwas originally obtained frommoist soils around greywater drains in uni-versity campus. The identification was made using standard taxonomickey and confirmed by plant taxonomist in university.

The urban wastewater was collected from a wastewater streamflowing over nearby location of university campus. The wastewaterwas collected from main streamline of wastewater drain in large-size pre-cleaned circular plastic containers of 20 L capacity. Collectedwastewater was brought immediately to laboratory and collected inlarge-size wastewater reservoir unit of the vermi-biofiltration sys-tem. Wastewater was collected just before the starting of experimen-tation in order to avoid alternation in the wastewater characteristicsmainly due to open storage of sample.

Other accessories like aeration pump, flow control units, waterpumps etc. were procured from a local sanitary engineering shopand scientific equipment supply firms.

2.2. Construction of vermi-biofiltration and biofiltration units

The experimental vermi-biofiltration /biofiltration units were com-prised of two reactors/batches: (i) long cylindrical unit: Reactor-I and(ii) rectangular unit: Reactor-II. Long unit was constructed with a tradi-tional water filtration system using gravels and sand column at the baseand a biofiltration system at the topmade of living individuals of wetlandplant stand, i.e. Cyprus rotundus and earthworms in its root zone system.An aeration unitwas alsofixed in themiddle layer of the Reactor-I. A plas-tic circular cylinder of 80 L capacity was used to construct Reactor-I ofvermi-biofiltration/biofiltration unit. Following materials/layers wereused to fill (from bottom to top) the circular cylinder to construct thevermi-biofiltration/biofiltration unit:

Layer I Large stones (10–15 cm in diameter) up to 5-inch — thislayer creates a kind of air chamber system and for water storagein base of system.Layer II Thick layer of small stones and gravel (5–7 cm diameter) upto 2-inch — acts as filtration unit and creates a kind of turbulenceduring water flow and provides space for aeration of wastewater.Aeration pipe (pierced 1 inch diameter and 15-inch length). Aera-tion pipe was covered with 1 inch layer of small pebbles. A fineplastic net was placed over the pebble layer — aeration devicewas installed in order to remove BOD load of the wastewater.Layer III A thick layer of sawdust spread over the net (2-inch) —

saw dust acts as good absorbent for several kinds of inorganic pol-lutants of wastewater.Layer IV Dried leaves of Sal tree were placed over sawdust layer(2-inch) — as natural adsorbent to remove nutrients from waste-water. It also acts as feed for microbial communities helping inwastewater mineralization.Fine net The fine plastic net (b0.5 mmpore-size)was placed over theleaf litter layer in order to check the entry of earthworm in deeplayers of the vermi-biofiltration system — in order to avoid movingearthworm to deep bottom layers of the reactor.

Layer V Vermi-biofiltration bed mainly constructed using thickbedding of soil mixed with small stones and pebbles along withcomplex root-zone system of surface plant Cyprus rotundus. Thethickness of this layer was about 10in. — earthworm acts as bio-logical agent to remove solid fractions of wastewater and mineral-ization of wastewater mainly driven by earthworm-microbeinteractions in root-zone system.Layer VI Composed of surface vegetation stand of Cyprus. It was about4 – 6 in. in length — wetland plant provides air in root-zone systemand removes nutrients fromwastewater through general absorption,adsorption and translocation processes. Also provides shelters tobeneficial microbial communities responsible for N mineralization.

The detail of vermi-biofiltration/biofiltration unit is given in Fig. 1.In the top layer of Reactor-I, i.e. Layer-V the fresh and viable speci-

mens of Cypruswere planted in top soil layers. The roots of plant wereplanted deeply and surface layer was irrigated regularly (for oneweek) by tapwater in order to fix the planted Cyprus in top layer of ver-mireactor. The mean density of Cyprus in vermireactor-I was about19plants/in.2. The open space between plant stand was filled with a thinlayer of small stone to avoid direct hydraulic impact on the plant andearthworm. In this vermi-biofiltration system efforts weremade to cre-ate a kind of soil ecological system mainly comprised of thick soil layerspiked with complex rooting system of Cyprus rotundus. The pieces ofstones and pebbles in this root-zone-filtration system create an appro-priate space for air and inoculated earthworm in sub-soil system. None-theless, the root-zone system not only enhances the efficiency ofwastewater filtration but at the same time also provide shelters to bac-terial communities (e.g., N-fixers, ammonifying and denitrification bac-teria) responsible for nutrient removal from wastewater.

Reactor-II: Another unit of reactor, i.e. Reactor-II was introduced inorder to enhance the removal efficiency of the system. In Reactor-IIthe biological component of the filtration unit was ofmore importancetherefore the majority of the reactor volume was filled with earth-worm and plant root zone layers. A rectangular plastic container ofsize (23. 5-inch length×18-inch width×15-inch depth) was used toconstruct the second unit (Reactor-II) of vermin-filtration system.In Reactor-II there were two district layers: firstly, base layer (largepebbles; 10–15 cm in diameter and height about 6-inches), and sec-ondly, top layer (small pebbles; 5–7 cm in diameter mixed with finesand and height up to 10-inches). The top layer acts as bedding sub-strate for earthworms in Reactor-II. A thin plastic net sheet was placedbetween the both layers to avoid movement of earthworms from toplayers to base layer of the vermireactor. Fresh and viable specimensof plant: Cyprus rotundus were planted in top layer and thin patchesof small stones were placed over the open spaces around Cyprusplant to avoid direct hydraulic impact of inflow water in Reactor-IIon plant stand and earthworms. Themean plant density in vermireac-tor was 0.14 plants/in.−2 (calculated using values of total surface areaof Reactor-II and plant numbers in reactors). After plantation Cyprusstand was allowed to grow for one week and during this period ade-quate amount of tap water was supplied in vermireactor to facilitatethe fixing of roots of plant in top layers of Reactor-II. Initially, bothreactors were run for two–three days using fresh tap water towash and fix the layers of vermibeds in proper functioning forms.After establishment of plant stands (after one week) the reactorwas run for wastewater treatment experimentations. In both exper-imental vermi-biofiltration systems, i.e. Reactor-I and Reactor-II indi-viduals of earthworm P. sansibaricus were introduced over thetop layer the reactors. Small passages were made in the surfacelayers of both reactors in order to facilitate worms to enter in thetop soil layers of the vermireactor. The initial earthworm density inboth vermi-biofiltration systems was measured in the ranges of22.0–24.5 g/L. The earthworms were allowed to settle in vermireac-tors for initial 2–3 days and thereafter, vermireactor was run for

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Outlet from Reactor-I

Aeration pipe

Aerator

Layer -VI

Layer - V

Layer - IV

Layer -III

Layer - II

Layer - I

Reactor -II

Outlet (completion of cycle

Layer -I

Layer -II

Layer -III

Reactor-IWastewater Tank

Water Sprinkling Device

Supply of wastewater from tank to reactor-I through pump

Fig. 1. Vermi-biofiltration system used for wastewater treatment.

Table 2Characteristics of wastewater used for experimentations.

Parameters Range

pH 7.61±0.10EC (ΩS/cm) 922.0±5.29TSS (mg/L) 216.67±7.64TDS (mg/L) 56813.3±51.3NO3

− (mg/L) 384.2±1.00PO4

3− (mg/L) 36.37±0.67COD (mg/L) 863.0±3.60

98 P. Tomar, S. Suthar / Desalination 282 (2011) 95–103

experimentation. A reactor without earthworm (bioreactor) acted asexperimental control for this study.

2.3. Observation and data collection

The wastewater was used without any dilation for this experimen-tation. However, prior to puttingwastewater in experimentation cyclea sample of wastewater (about 1 L) was separated from stock and an-alyzed for its physic-chemical characteristics (Table 2). As illustratedin Fig. 1, during experimentation cycle the stock wastewater was sup-plied in Reactor-I through a mechanical pump and a flow control devicewas also fixed inmainwater-supply pipe. Thewastewaterwas sprinkledover the surface of top layer of Reactor-I through a perforated plastic pipeand outlet of Reactor-Iwas closed to fill the reactorwithwastewater. Thewastewater was filled in reactor continuously up to the saturation level

of top layer, i.e. layer-V. The care was taken to avoid the overflowing ofwater. The wastewater was retained for 1 h in Reactor -I and a continu-ous air was supplied during this period using an electronic aeration de-vice. After that the outlet of Reactor-I was opened into Reactor-II and

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8.4

8.2

8

7.8

7.6

7.4

7.2

7

6.80 1 2 3 4 5 6 7 8

pH

Treatment cycle

ExperimentControl

Fig. 2. Changes in pH during different cycles of treatment in control and experimentalreactor.

1400

1300

1200

1100

1000

900

800

700

6000 1 2 3 4

Treatment cycle

EC

5 6 7 8

ExperimentControl

ΩS/

cm

Fig. 3. Changes in EC during different cycles of treatment in control and experimentalreactor.

99P. Tomar, S. Suthar / Desalination 282 (2011) 95–103

flowof outletwas controlled using amechanical flow control device. Theoutlet water from Reactor-I was sprinkled over the surface of Reactor-IIusing a perforated pipe system. In second cycle of treatment (i.e., treat-ment in Reactor-II) the water retentionmechanism and time frameworkwas same as used in Reactor-I. After that the outlet of Reactor-II wasopened to release thewater from second reactor, i.e. Reactor-II. The com-plete passing of water from both reactors was counted as one treatmentcycle and water after each cycle was putted back into new cycle. Thewastewater was repeatedly passed through both units of vermifiltrationsystem for complete 8 cycles. An interval (stabilization period) of 24 hwas kept between two subsequent treatment cycles in order to stabilizethemicrobial environment and earthworm population in sub-surface ofthe vermireactor after each cycle. A sample ofwastewater was collectedin pre-cleaned and sterilized polythene bottle of 1 L capacity fromoutletof Reactor-II after each treatment cycle and stored at 4 °C for further in-vestigations on changes in physico-chemical characteristics of waste-water during each cycle.

2.4. Chemical analysis

The chemical characteristics of wastewater samples collected aftereach treatment recycle were analyzed for different physic-chemical pa-rameters by following methods as described by APHA-AWWA-WPFC[30]. pH was measured using digital pH meter (Metrohm, Swiss-made).Conductivity was measured using digital conductivity meter (Remi,India). Total dissolved solids (TDS) and total suspended solids (TSS)was measured was measured filtration and gravimetric and oven dryingmethods. Chemical oxygen demand (COD) was measured using po-tassium dichromate oxidation method. Nitrate, sulphate and phos-phate contents in water were analysed spectrophometrically byfollowing methods as described by APHA-AWWA-WPFC [30].

2.5. Statistical analysis

A paired sample t-test between control (without earthworm) andexperimental (with earthworm) vermi-biofiltration unit was per-formed for each chemical parameter to analyze the differences.One-way analysis of variance (ANOVA) was also preformed to mea-sure the difference among different cycles for each physic-chemicalparameter of wastewater. SPSS® statistical package (Window Version13.0) was used for data analysis. All statements reported in this studyare at the pb0.05 levels.

3. Results and discussion

The quality of wastewater in terms of phyico-chemical character-istics is described in Table 2. The collected sample of urban wastewa-ter showed relatively high values of some key pollution indicatingparameters of water: TDS (50813 mg/L), NO3

− (384.2 mg/L), PO42−

(36.37 mg/L), SO42− (293.3 mg/L) and COD (863.3 mg/L). The waste-

water after vermi-biofiltration process showed a drastic change inits major physico-chemical parameters, after each treatment cycle.Although, there was significant reduction in key pollutants of urbanwater in both biofiltration (without earthworm) and vermi-biofiltration(with earthworm), but difference was more prominent in water fromvermi-biofiltration unit than initial levels. The changes in all reactorscould be attributed to the development of biological communities with-in reactors [26].

3.1. pH

The change in pH during different treatment cycle is illustrated inFig. 2. In biofiltration system (control) a trend of slight increment inpH was observed till last observation. On the other hand, in vermi-biofiltration system pH decreased sharply up to 3 rd cycle of treat-ment thereafter, a trend of gradual increment was observed up to

7th cycle followed by pH stabilization state during last treatmentcycle. pH of water mainly depends upon a variety of chemical factors,e.g., dissolved gases, organic acids, humic fractions and inorganicsalts. The decomposition of organic fractions of wastewater, mainlyby microbes in water, produces some acidic species of mineralized or-ganic materials (CO2, ammonia, NO3

− and organic acids) which playsan important role in shifting of pH scale of treated water. Probablythe reduction in the level of ammonia, NO3− during biofiltration andvermi-biofiltration treatment caused sight changes in pH. There wasstatistically significant difference between biofiltration and vermi-biofiltration process for pH level (t-test: pb0.05) of effluent from reac-tors. The pH value of effluent obtained at the end of treatment processwas 7.81 in biofiltration (about 9.1% more than initial) and 8.15 invermi-biofiltration (about 13. 8%more than initial) reactor. The differ-ent between control and experimental reactor for pH could be relatedto earthworm mediated rapid mineralization of organic fractions ofwastewater. Also few earlier researchers have reported increase inpH after vermi-biofiltration processes [19, 21].

3.2. Electrical conductivity (EC)

Electrical conductivity (EC) ofwastewater showed significant changesafter treatment through filtration system in both biofiltration and vermi-biofiltration processes. The conductivity of treated water was: 1230.0ΩS/cm in biofiltration and 984.7ΩS/cm in vermi-biofiltration system. Thedifference between control and experimental reactor was statisticallysignificant (t-test: p=0.002). The changes in EC during different cyclesare described in Fig. 3. In biofiltration system EC showed a linear trendof increase till last observation while in vermi-biofiltration reactor ECshowed different patterns of fluctuation during experimental processes.In vermi-biofiltration system EC value of effluent showed increasingpattern up to 5th cycle of treatment thereafter, it reduced sharply tilllast observation. The increasing EC could be attributed tomineralizationof organic waste fractions of wastewater through microbial and

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earthworm activities in reactors. The higher EC of effluent from vermin-biofiltration than experimental control was possibly due to highminer-alization processes driven by inoculated worm community in reactor[31]. In general, when organic waste transits through earthwormgut some fraction of it is then converted into plant available forms[25]. Probably the release of different mineral ions, such as phosphate,ammonium and potassium results in increased EC of substrate. TheEC reflects the salinity of any material and it is a good indicator ofthe mineralize fraction of wastewater. However, after 5–6 cycles oftreatment EC of effluent water from vermi-biofiltration reactor showedsharp decrement till last observation. This could be due to adsorptionand/or absorption of inorganic constituents ofwater by different biolog-ical or non-biological components [32] of vermi-biofiltration system.Moreover, accumulation of salts by inoculated worms, during later fil-tration in vermi-biofiltration process, might be responsible for reduc-tion in EC.

3.3. COD

COD is an important indicator of organic load of urban wastewater.The COD load in effluents from biofiltration and vermi-biofiltration sys-tem was significantly low than initial levels, but vermi-biofiltrationshowed more removal efficiency than biofiltration reactor (t-test:pb0.001). The removal rate was 90% (as compared to initial level) invermi-biofiltration system and 36.8% in biofiltartion system. Thiscould be because earthworms and aerobic microbes act symbioticallyto accelerate and enhance the decomposition of organicmatter [33]. Re-sults clearly indicated the potential of worms in removal of organic loadfromwastewater through direct feeding of solid fractions of water or bypromoting microbial-mediated organic decomposition process. TheCOD removal rate was 84% in vermi-biofiltration system after comple-tion of 8 cycles of treatment. The changed in COD load of wastewaterduring different treatment cycles is illustrated in Fig. 4. In control biofil-tration system COD reduced gradually during treatment cycles while invermi-biofiltration system COD level of effluent water reduced rapidlyafter 1st treatment cycle (Fig. 4). Earlier worker have also reported sig-nificant reduction in the COD load during biofiltration and vermi-biofiltration processes [3, 21]. Sinha et al. [3] studied the vermifiltrationofwastewater originated fromdairy industry under a pilot-scale project.They claimed the average COD reduction in the ranges of 80–90% at theend. Under another laboratory trial of urban wastewater treatmentthrough vermifiltration, Sinha and his associates reported about 45% re-duction in COD load after treatment [19] and removal rate was signifi-cantly high in experimental reactor than control one (without worms).In general, the geological and microbial system in control biofiltrationunit is responsible for COD reductionwhile in vermi-biofiltration systemenzymes, secreted by earthworm and gut-associated microflora, reducethe those chemicals which otherwise cannot be decomposed by mi-crobes [19, 25]. Recently Xing et al. [21] have reported significant COD

Fig. 4. Changes in COD during different cycles of treatment in control and experimentalreactor.

reduction (47 – 58% than initial) during vermi-biofiltration of domesticwastewater. Also Ghatnekar et al. [18] have investigated the impact ofvermi-biofiltration system on chemical characteristics of wastewatergenerated from gelatin industry. They claimed about 90% reduction inlevel of COD at the end of process. Wang et al. [5] also reported90.2% average removal efficiencies of vermi-biofiltration system forCOD of a domestic wastewater. The microbial association with wormsin vermifiltration system could be important for removal of organicload form wastewater. The presence of earthworm also promotes themicrobial colonization in vermibeds and evidences from recent investi-gation supports this hypothesis [2, 34]. Zhao et al. [2] investigated theearthworm-microorganism interaction during wastewater sludgetreatments and results suggested about 46% reduction in the contentsof volatile suspended solids due to earthworm-microbial action aftertreatment process. The easy assimilable source of carbon and otheravailable nutrients from earthworm products, i.e. casts and mucus ac-celerates the microbial colonization in earthworm-containing vermi-beds. According to Singleton et al. [35] earthworm hosts millions ofdecomposer microbes in their gut and excreate them in soil alongwith nutrients inworm casts. Such nutrients further enhance themicro-bial quality and quality of the vermibeds. Moreover the formation ofbiofilms of decomposer microbes in the geological system of the ver-mireactor also promotes COD reduction during vermifiltration process[3]. Chiarawatchai andNuengjamnong [36] and Chiarawatchai [26] sug-gested that earthworms contributed to the wastewater remediationduring the treatment process within the VSFCWs. Results thus, clearlyindicate that vermi-biofiltration may be an efficient treatment tool fordesigning of a low-cost domestic wastewater treatment facility.

3.4. NO3−–N

Nitrate is an important indicator of water pollution and its highconcentration in freshwater bodies leads to eutrophication problem.In this study there was significant impact on nitrate concentrationin effluents after treatment in both experimental reactors. But NO3

reduction arte was prominent in vermi-biofiltration unit than biofil-tration system (Table 3). The level of NO3

− in effluent after final treat-ment cycle was 27.9 mg/L for vermi-biofiltration unit and 186.9 mg/Lfor biofiltration unit. There was about 92.7% total removal of NO3

−–Nin vermi-biofiltration unit that was significantly higher than total re-moval in biofiltration unit (51.3% removal) (t-test: pb0.001). In tradi-tional wetland biofiltration system the nutrients and metals may beremoved from the polluted water and retained in the sediment andtaken up by the plants and by microorganisms associated on the sur-face of the roots and sediments, by immobilization in sediments via.,mechanism such as adsorption on ion exchange sites binding to or-ganic matter, incorporation into lattice structure and precipitatesinto insoluble compounds [37]. The results of removal efficacy of bio-filtration system were similar to those observed in constructed wet-lands by other researchers [28, 32] and were moderately higherthan those detected in horizontal flow constructed wetlands planted

Table 3Chemical characteristics of outlet frombiofiltration (control reactor) and vermi-biofiltration(experimental) at the end of process.

Parameters Controlreactor a

Experimentalreactor b

t-test c

(t-coefficient value)Significancelevel

pH 7.81±0.01 8.15±0.01 51.50 Pb0.001EC (ΩS/cm) 1230.0±8.0 984.67±11.7 −22.86 P=0.002TSS (mg/l) 78.40±1.00 24.8±2.82 −1179.71 Pb0.001TDS (mg/l) 9875.0±15.0 91.3±5.13 −26.113 Pb0.001NO3

− (mg/l) 186.90±1.02 27.92±2.93 −69.55 Pb0.001PO4

3− (mg/l) 12.67±0.03 0.62±0.04 −374.86 Pb0.001COD (mg/l) 545.6±5.0 86.67±2.03 −160.93 Pb0.001

a Reactor without earthworms (vermi-biofiltration).b Reactor with earthworms (biofiltration).c Paired sample t-test between control and experiment.

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101P. Tomar, S. Suthar / Desalination 282 (2011) 95–103

with Phragmites by Vymazal [38] and with Canna and Heliconia byKonnerup et al. [39]. The high NO3

−–N removal efficiency of currentbiofiltration system than previous reports could be explained interms of oxygen supply in rhizosphere of biofiltration system. In gen-eral, oxygen is released by roots of plants in constructed wetlands andit should be sufficient to meet the demand for the aerobic bacterialcommunities which are mainly responsible for NO3

−–N removalfrom wastewater. Therefore, addition of aeration device in currentbiofiltration system was an advantage over traditional biofiltrationor wetland filtration systems. Vymazal [38] also pointed out that inmost system designed for the treatment of domestic or municipalsewage the supply of dissolved organic matter is sufficient and aero-bic degradation is limited by oxygen availability. The supply of oxy-gen also promotes the activities of heterotrophic and ammonifyingbacteria which are mainly responsible for nitrate removal fromwastewater. In general, denitrification processes involved the initialNO3–N reduction to NO2–N, followed by further reduction to nitricoxide (NO), nitrous oxide (N2O) and finally to molecular nitrogen(N2) [40]. However, NO3

−–N reduction rate was relatively high inthis study than previous reports and probably that attributed to oxy-gen supply in the system. Wang et al. [5] reported efficient removal ofNH4

+–N (with 85.7–97.1% of removal rate) while studying wastewa-ter treatment using an earthworm-based ecological filter integratedconstructed rapid infiltration (Eco-CRI) system. Xing et al. [21]reported about 7.63 to 14.9% total N and 21.0 to 62.3% NH4–N removalin wastewater after treating through vermi-biofiltration system. Thedifferent between biofiltration system and vermifiltration system forremoval rate should be explained in terms of the population and activ-ities of nitrogenmetabolizing bacteria. Chiarawatchai [26] reported sig-nificant reduction in level of nitrate in effluents obtained from a lab-scale microcosm wastewater treatment unit than effluent from reactorwithout worms. The presence of earthworm in rhizosphere sub-systemhas some advantages over traditional biofiltration system because ofthe direct impact of earthworms on aerobic heterotrophic bacterialcommunities which are mainly responsible for N-mineralization inwastewater biofiltration systems. The trend of changing NO3

− -N levelduring the treatment cycles is described in Fig. 5. There was rapid re-moval in vermi-biofiltration unit than the biofiltration unit in the firstand second cycle of the treatments and that could be due to filtrationof suspended substances during first cycle of treatment which are con-sidered to be feed materials for earthworms in vermi-biofiltration sys-tem. Moreover, earthworm-mediated rapid nitrogen transformationleads to rapid NO3

− -N loss from wastewater.

3.5. Phosphate (PO43−)

As described in Table 3, there was significant different betweeninlet and outlet water for PO4

3− concentration in both treatment reac-tors, i.e. biofiltration and vermi-biofiltration. The source of phosphate

Fig. 5. Changes in NO3− during different cycles of treatment in control and experimental

reactor.

in wastewater is household drains and urban runoff water containingexcreta and other organic substances [21]. The final effluent from vermi-biofiltration system showed low concentration of PO4

3− (0.62 mg/L) thansample collected from final stage of biofiltration system (12.67 mg/L).The PO4

3− removal efficiency of vermi-biofiltration was recorded 98.3%and that was significantly higher than removal efficiency of biofiltrationsystem (65.2%) (t-test: pb0.001). The patterns of PO4

3− removal duringdifferent treatment cycles is described in Fig. 6. It is clear that in biofiltra-tion system the removal trend for PO4

3− is slow and linear but in vermi-biofiltration reactor there was a trend of sharp PO4

3− removal up to5–6 cycles of treatments thereafter; removal rates declined sharply.The ligand exchange reactions and physical adsorption or sorption sitesrapidly removes phosphorous from the soil solution. In soil column thehydroxides and oxides of Al and Fe, calcium carbonate and layer silicateminerals are important sites for sorption of phosphate anions [41, 42].The PO4

3− removal efficiency of current biofiltration systemwith Cyprusstand was relatively higher than those detected in horizontal flow con-structed wetlands planted with Phragmites by Vymazal [38]. In currentvermifltration system the top layer composed of sandy soils alongwithmixtures of large stones and pebbles. Probably the sandmixed col-umn of current biofiltration reactor was advantage over the previousbiofiltration systems. Preetha and Kumar [43] demonstrated morethan 99% removal of PO4

3− from wastewater using sand-column treat-ments device. According to Bostrom et al. [44] aerobic conditions aremore favourable for P sorption and co-precipitation therefore; it is sug-gested that high PO4

3− removal could be due to addition of aeration de-vice in our vermi-biofiltration system. However, results of phosphorusremoval contrasts with finding of Chiarawatchai [26] who reportedleast impact of earthworm inoculation on phosphorous removal fromwastewater during vermi-biofiltration process. He suggested sometechnical improvements like replacement of substrates from gravel orsand to ones with high phosphorus adsorption capacities to enhancephosphorous removal capability of vermi-biofiltration unit. However,better results of this study than previous report could be attributed tosubstrate quality, design and biological components (earthworm spe-cies, plant type etc.). Moreover, activities of earthworm and associatedmicroflora in vermibeds also promote rapid P-mineralization in the sys-tem. The level of PO4

3− in treated effluent from biofiltration and vermi-biofiltration is of prime concern because high concentration of suchsubstance is responsible for eutrophication in surface freshwater re-sources. Although, the level of PO4

3− in final effluent from biofiltrationsystem was comparatively high than prescribed limit, i.e. 5.0 mg/L asdecided by national pollution monitoring agency, i.e. Central PollutionControl Board (CPCB) for surface discharges of treated water.

3.6. TSS and TDS

Total suspended solids (TSS) and total dissolved solids (TDS)showed drastic reduction during biofiltration and vermi-biofiltration

Fig. 6. Changes in PO43− during different cycles of treatment in control and experimen-

tal reactor.

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Fig. 7. Changes in TSS during different cycles of treatment in control and experimentalreactor.

Fig. 9. Changes in different parameters of wastewater during different cycles of treat-ment in control and experimental reactor.

102 P. Tomar, S. Suthar / Desalination 282 (2011) 95–103

process (Fig. 7 and 8, respectively). The total reduction in TDS contentwas about 99.8% in vermi-biofiltration unit and that was significantlyhigher than total removal in biofiltration system, i.e. 82.6% (t-test:pb0.001). Results thus clearly suggested the capability of earthwormsto remove solid fractions of wastewater during vermi-biofiltrationprocesses. Similarly TSS also reduced significantly in wastewaterobtained from both experimental reactors (biofiltration and vermi-biofiltration) at the end of process. The removal rate was high invermi-biofiltration unit (88.6% than initial level) than biofiltrationsystem (63.8%) (t-test: pb0.001) (Table 3). The removal pattern ofTDS in both filtration systems is described in Fig. 7. The control (bio-filtration) system showed a gradual removal of TDS during differentcycles of treatments process while in vermi-biofiltartion system TDSremoved sharply during initial 3–4 cycles thereafter; the removalprocess was more or less steady till last observation. The differencebetween both systems could be due to difference in biological compo-nents and working capabilities of both reactors. According to Cooperet al. [45] and Vymazal et al. [46] the suspended solids that are not re-moved in pre-treatment system are effectively removed by filtrationand settlement processes. Mustafa et al. [47] reported the potentialof integrated constructed wetland system with Typha latifolia, Carexriparia, Glyceria maxima, Philarius arundiraecae and Juncus effuses inwastewater treatments. They have reported significant removal ofTSS, i.e. 93.7% after treatment process. According to a study conductedby Prabu and Udayasoorian [28] Phragmitis australis, Cyperus pangoreiand Typha latifolia planted biofiltration system removed about 77, 72and 67%, respectively TSS fromwastewater after treatments. The effica-cy of vermi-biofiltration system in TDS and TSS removal is also reportedby earlier authors. Sinha et al. [3] reported total removal of TSS and TDSin the ranges of 90–92% and 90–95%, respectively. They have attributedthe TSS removal to continuous consumption by earthworms. Xing et al.[21] demonstrated the results of a small-scale vermifiltration unit for

Fig. 8. Changes in TDS during different cycles of treatment in control and experimentalreactor.

domestic wastewater treatment. According to this study earthwormpresence in treatment system caused about 57 to 79% reduction intotal content of suspended solids in wastewater. The results of presentstudy corroborates with the findings of other scientists who claimedimportance of earthworm in vermifiltration system. However, more de-tailed is needed to establish the relationship between removal of solidsand earthworm working mechanism in vermi-biofiltration system.

4. Conclusions

This work provides an opportunity to explore the efficiency of avermi-biofiltration system (mainly constructed by using a wet-land weed Cyprus rotundus and live biomass of a local earthwormP. sansibaricus) in treatment of urban wastewater. Earlier scientificapproaches were based upon the use of either plant or earthworm inbiofiltration unit design. But in this study the integration of these twocomponents (traditional constructed wetlands system and earthwormshas been applied to design a cost effective and sustainable option foronsite wastewater treatment. Results clearly suggested that integratedvermi-biofiltration reactor was more efficient than traditional biofiltra-tion system in terms of removal of key chemical pollutant from waste-water (Fig. 9). Although, results clearly indicates the efficacy of vermi-biofiltration system in wastewater treatment but further detailedstudies are still required to answer few key issues of this system,e.g. hydrolic load, retention time impact, microbial ecology in ver-mibeds, earthworm-microbial interaction etc.

Acknowledgement

We would like to thank four anonymous reviewers for critical com-ments and fruitful suggestions on earlier version of the manuscript. Thekind cooperation of laboratory staffs (Mr. Ganesh Bahuguna, NamitaTiwari, Kamal and Digpal Negi) during experimentation is also acknowl-edged here.

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