Performance of Submerged Fixed-bed Biofilm Reactor Packed with Black Scoriafor Municipal Wastewater Treatment

Zahid, W. and El-Shafai, S1

Civil Engineering Department, College of Engineering, King Saud University, P.O. Box 800,Riyadh 11421, Saudi Arabia, E-mail: selshafai@ksu.edu.sa; wmzahid@ksu.edu.sa

1 Permanent address: Water Pollution Research, National Research Centre, El-Behous Street,Dokki, Giza, Egypt

22nd Joint GCC-Japan Environment SymposiumSustainable GCC Environment-Challenge for our Future

5th Joint KFUPM-JCCP Environment SymposiumMarch 03-05, 2014

King Fahd University of Petroleum & Minerals, Dhahran 31261, Kingdom of Saudi Arabia

Introduction

Objectives

Materials and Methods

Results and Discussion

Conclusion

Acknowledgment

Future plan

Sanitation coverage in Saudi Arabia

In Saudi Arabia many areas still lack sanitation systems for effective treatment of domesticwastewater.

55% of the population have no access to sewerage networks (Ministry of Economy and Planning,2007)

In 2010, 1250 million m3/year of domestic wastewater disposed of in private onsite treatment units

Comparing to that only 1185 million m3/year of MWW collected in sewer pipelines (Al-Saud, 2010).

Some of the existing MWWTP need rehabilitation and upgrading to meet the strict Saudi standard.

NWC is planned to spend around $24.8 billion allocated budget in wastewater section.

This investment aims to increase wastewater network coverage to 100% (Abderrahman, 2010).

The KSA has specific horizontal distribution pattern of the population throughout the country, whichmakes it difficult and expensive to build central WWTP with very long sewer networks.

Decentralized facilities cost less and represent very prominent solution for many regions in thekingdom.

There are many types of decentralized units that can be used as a treatment solution for MWW.

However, many of them in need for skilled personnel, which is a challenge for many decision-makers.

Mostly, in many developing countries, decision makers are looking for the technology that is simplein operation and produce good treated effluent.

Submerged biofilm reactors as robust technology

In Saudi Arabia, treatment performance of up-flow submerged biofilm reactor has not beeninvestigated yet.

Submerged biofilm reactors are very effective and efficient in organic carbon and nitrogenremoval

The SBRs exhibit lots of advantages as compared with activated sludge process such as:

Stability and long SRT which enable removal of recalcitrant pollutants

Much higher biomass content in terms of MLSS and MLVSS

Much less surplus biomass or sludge with good settling properties

The good settling properties is attributed to the longer SRT

High biomass concentration allow operation at low hydraulic retention time which results in lesssystem footprint

The submerged biofilm reactors with single or different ecological zones, is less expensive thanthe moving bed biofilm reactor.

The moving bed biofilm reactor needs high energy input to keep the moving media suspendedand in continuous circulation within the reactor.

The range of air flow rate to keep the media in suspension is 0.83 L/L per minute (5% fraction)to 1.5 L/L of the reactor volume per minute (20% fraction); (Lee et al., 2006).

The submerged biofilm reactor is promising technology that has been used for the treatmentof municipal wastewater, industrial wastewater and dairy wastewater

Up-flow submerged biofilm reactor represents very robust, flexible and compact system withlow sludge production and low maintenance cost.

The system can be built at any scale

It could be installed in existing activated sludge treatment facilities that have overloadproblem.

There are vast fields of substantial basaltic flows covering an area of approximately 100,000 km2 in thewestern part of Saudi Arabia.

These fields, locally known as Harrat (Arabic name) form spectacular volcanic landforms

along the eastern shore of the Red Sea.

1. Harrat Rahat

2. Harrat Al Harrah

3. Harrat Ar Raha

4. Harrat Uwayrid

5. Harrat Hutaymah

6. Harrat Kishb

7. Harrat Khaybar

8. Harrat Ithnayn

9. Harrat Lunayyir

10. Harrat Al Birk

11. Jabal Yar

Harrat Al Harrah

Basaltic scoria or cinder cones is the second largest component of

the volcanic landforms

The scoria cones are largely composed of basaltic fragments

Based on the average specific gravity, Scoria is lightweight aggregate

Although these deposits are generally denser than the pumice, they have good market asaggregates for road construction

Scoria has potential for manufacturing of light weight and heat insulated building blocks

Scoria is used for pozzolan cement production and preliminary results of horticulturalapplications of scoria are encouraging.

Scoria is somewhat porous material with high surface area and strength with densitylarger than 1.

Scoria is an excellent media which holds water in its pores and allow air circulation to theroot zone of the plant.

The volume of the deposit is sufficiently large to warrant economic exploitation.

The general geomorphic features of the area provide suitable conditions for easyexcavation and processing of the deposits

1. Objective:

I. Application of single up-flow aerobic submerged biofilm reactor and single up-flowanaerobic/aerobic submerged biofilm reactor packed with local scoria as biofilm carrier formunicipal sewage treatment

II. Study effects of effluent recycle on the treatment performance in both

2. Materials and Methods

2.1. Reactor configuration

The reactor was made of PVC column with 14.5 cm ID, 65 cm total height and 63.6 cm workingheight

The reactor has 10.5 L total working volume

The Reactor was divided into three zones (upper, middle and lower zone)

A perforated PVC disc with 20 evenly distributed pores was fixed at 3.6 cm from the bottom tosupport biofilm carrier (scoria)

The middle zone was packed with Scoria with 0.49 void ratio

Air diffusers (shown in Figure)

A 3 liter settling tank was used to separate detached biomass that is released with the treatedeffluent

Effluent recycling (shown in Figure)

On

Off Dosing pump

(in case of effluent recycle)

2.2. Reactor operation

To enhance biofilm growth, the reactor was inoculated with 4.36L of return sludge from anactivated sludge municipal wastewater treatment plant in Riyadh.

The sludge has 10.12 g MLSS/L and 6.84 g MLVSS/L.

After inoculation, the reactor was fed with screened sewage from King Saud UniversityWWTP at 25ml/minute for 17 days; start-up period.

After start up, the reactor was operated at six different operational cycles as in Table 1.

Hydraulic Loading Rate (HLR) was calculated based on the total reactor volume. TheoreticalHydraulic Retention Time (HRT) was calculated based on the measured Flow Rate (FR) andtotal volume of the reactor.

Water volume (5.78L) in the reactor was used to calculate the actual HRT. The air flow ratewas fixed at 1.0-1.5 L/minute by using air flow meter.

During the time of operation the dissolved oxygen concentration of the water phase in theupper zone of the reactor was never lower than 5mg/L.

Table 1: Operatingconditions during the operational cycles

Item Aerobic biofilmcyclesAnaerobic/aerobic biofilmcyclesLow HLR High HLR

Operational cycle Cycle 1-1 Cycle 1-2 Cycle 2-1 Cycle 2-2 Cycle 2-3 Cycle 2-4

50% effluent recycle No Yes No Yes Yes No

Measured FR (ml/minute) 25.8± 2.7 29.1±2.8 26.4±2.6 24.5 ±1.6 38.4± 2.6 38.8 ±1.5

HLR(L/L/day) 3.5±0.4 4.0±0.4 3.6±0.4 3.4±0.2 5.2± 0.4 5.3±0.2

Theoretical HRT(hrs) 6.78 6.01 6.63 7.14 4.56 4.51

Actual HRT(hrs) 3.73 3.31 3.65 3.93 2.51 2.48

Operational period (days) 35 14 26 24 25 17

2.3. Analytical procedure

Water sampling

Analytical parameters (pH, DO, COD, Turbidity, TSS, Ammonia N, Nitrite N, Nitrate N, TKN, TPand Alkalinity all the analyses were carried according to The Standard Methods for theExamination of Water and Wastewater (APHA, 2005).

Onsite measurement of water temperature and flow rate was carried out daily.

Settled sludge in the secondary sedimentation tank was sampled on disposal and analyzed forSV and SVI

2.4. Statistical analysis

Data was subjected to one way analysis of variance (One- way ANOVA) to check the significantdifferences between the treatment cycles

3. Results and Discussion

3.1. Characteristics of raw wastewater (Table 2)

There was a variation in the characteristics of raw influent

The influent has a temperature range of 16-36 oC while the pH range was 7.4-7.9.

Experiments extended between mid of February to the end of July 2012.

Sewage strength was medium for COD&TSS and little higher for TKN during start up and cycles 1-1, 1-2, 2-1

The sewage strength was between low and medium for COD, TSS and medium for TKN in cycles2-2, 2-3, 2-4

The variation is mostly attributed to seasonal variation in water consumption and temperature effects.

Table 3: Characteristics of the treated effluent during the start up period

The system was able to produce effluent with satisfied COD, turbidity and TSS concentrations.

The corresponding removal values were 90% COD, 94% turbidity and 95% TSS.

Nitrite accumulation episodes happened during the start up period (average conc. Of NO2 >NO3)

A faster growth of ammonium oxidizers than nitrite oxidizers.

By the end of the period, the system was able to remove 74 and 73% of the ammonia and TKN

TN removal was limited to 24% because of the residual nitrite and nitrate (4.48 & 7.3 mgN/L)

COD removing biofilm or simply heterotrophic biofilm is growing faster than nitrifying biofilm

Efficiency during the start up period

Treatment efficiency during the aerobic cycles

Table 4: Characteristics of the treated effluentTable 5: % removal of contaminants

1. The results show satisfied effluent quality fororganic matter removal during the two cycles

2. The residual values of ammonia and TKN were lowin cycle 1-1

3. The percentages removal of the contaminants aregood specially during this cycle (1-1)

4. The ammonia and TKN removal were 97%and 96% for both respectively in cycle 1-1

5. Effluent recycle in 1-2 has dramaticallyaffects the residual ammonia and TKN

6. The recycling of the effluent enhanceammonification rather than denitrification

7. The recycling slightly affects the COD, TSSand turbidity of the effluent

8. Effluent recycling enhances TP removal

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stop recyclebetween 1-2 and 2-1

Figure 2: Nitrogenconcentrations inthe effluentduring theoperational cycles

Removal efficiency of ammonia, TKN and TN dramatically reduced from 97, 96 and69% to 57, 66 and 50% respectively.

Nitrate concentration was reduced from 13.5 to 7.5 mgN/L

The average ammonia concentration was increased from 1.4 to 17.0 mgN/L.

By stopping effluent recycling, ammonia and nitrite concentrations were reduced to1.6 and 1.07 mgN/L, respectively while nitrate was increased to 13.7 mgN/L within 24hours (Figure 2).

Table 6: Characteristics of the treated effluent

Treatment efficiency during the anaerobic cycles

At low HRT and Low Hydraulic loading rates (2-1 and 2-2)

The system provides good quality effluent specially with effluent recycling (2-2)

Residual values of the contaminants were significantly low with effluent recycling (2-2)

At low retention time and high hydraulic loads (2-3 and 2-4)

With effluent recycling (2-3), the residual values of the contaminants have not been affected

Table 7: % removal of contaminants

Treatment efficiency during the anaerobic cycles

Effluent recycling significantly enhance N removal percentages in both cases (low and highHRT)

Lowering the HRT and increasing the HLR significantly reduce removal of TP

Lowering the HRT and increasing HLR moderately affect the removal of OC

Operational cycles Aerobic cycles Anaerobic/aerobic cyclesParameter Unit Cycle 1-1 Cycle 1-2 Cycle 2-1 Cycle2-2

Temperature oC 15-25 22-25 26-36 31-37pH - 6.9-7.7 6.9-7.8 6.4-7.2 6.8-7.8DO mgO2/L 7.1±0.7 6.8±0.6 6.1±0.5 6.1±0.2COD mgO2/L 34.8±7.0ac 42.9±9.4a 33.9±12.0c 23±11c

Turbidity NTU 6.4±2.6a 9.0±6.1a 2.9±1.4c 1.9±1.0c

TSS mgO2/L 8.1±3.4a 11.8±7.6a 3.2±1.4c 3.1±1.9c

Ammonia mgN/L 1.4±1.4a 17.0±11.4b 3.5±1.8c 0.3±0.3d

Nitrite mgN/L 1.53±1.09ac 1.79±0.42a 1.16± 0.6c 0.21±0.12d

Nitrate mgN/L 13.5±4.1ac 7.5±3.6b 13.1±3.0c 8.1±2.1db

TKN mgN/L 2.3±1.2a 19.6±12.7b 4.5±2.6c 1.8±0.7d

TN mgN/L 17.5±5.4ac 28.9±9.7b 18.8±5.0c 9.9±1.8d

TP mgP/L 3.91± 0.43 3.51±0.30 3.52±0.53 2.86±0.89Alkalinity mgCaCO3/L 57±30 176±84 48±10 76±37

Aerobic versus anaerobic

Without effluent recycling (1-1 versus 2-1)

There was no significant differences between both in case of COD, Nitrite and Nitrate

For TSS and Turbidity there was significant reduction in case of anaerobic comparing to aerobic cycle

On the other hand ammonia and TKN were significantly increased in case of anaerobic cycle

For TN there was no significant differences

In case of effluent recycling (1-2 versus 2-2):

The treated effluent of the anaerobic cycle (2-2) have significantly lower values for all except nitrate (no difference)

Table 8: aerobic versus anaerobic

Without effluent recycling (1-1 versus 2-1)

There was no significant differences between both in case of COD and TN

Anaerobic cycle has significant higher removal for turbidity and TSS

On the other hand ammonia and TKN removal were significantly low

For TN there was no significant differences

In case of effluent recycling (1-2 versus 2-2):

The treated effluent of the anaerobic cycle (2-2) have significantly higher removal for all parameters exceptTP (no difference)

Table 9: Aerobic versus anaerobic

Table 10: National Reuse Standard in Saudi Arabia and Egypt

The system of anaerobic/aerobic submerged fixed-bed biofilm provides effluent compliedphysico-chemically with the water quality criteria of tertiary treated effluent according to Saudiand Egyptian standards specially under effluent recycling

3.2.4. Sludge productionThe system produces sludge with good settling properties especially in case of anaerobic/aerobic reactorwhere the average values of SVI were 56±12 ml/g and 33±14 ml/g during the aerobic andanaerobic/aerobic cycles, respectively.

During the whole period of this study the average total sludge production was 0.145 g TSS/g CODremoved with a range from zero to 1.072 gTSS/gCOD removed.

During the aerobic cycles the total sludge production was 0.205 g TSS/g COD removed on average.

This sludge production rate was highly reduced during the anaerobic/aerobic cycles to an average valueof 0.017 g TSS/g COD removed.

This shows that the single anaerobic/aerobic reactor provides less sludge production with better settlingproperties which makes it more superior to the single aerobic reactor.

The nitrogen content of the excess biomass was in the range of 4.9-5.3% of the MLSS.

The range of solid loading rate to the secondary clarifier ( 0.00- 1.47kgTSS/m2.day) is far below therecommended value (Metcalf and Eddy 2003).

In this study, the daily average solid loading rate to the clarifier was 0.185 kg TSS/m2.day while the rangeof surface loading rate to the clarifier was 3.5-5.4 m3/m2.day.

4. Conclusions

Single anaerobic/aerobic up-flow submerged biofilm reactor packed with local scoria provide goodquality effluent complied physico-chemically with the water quality criteria of tertiary treated effluentaccording to Saudi and Egyptian standards

Effluent recycling in the aerobic reactor did not improve ammonia and TN removal while effluentrecycling in the anaerobic/aerobic reactor enhanced ammonia and TN removal.

Application of single anaerobic/aerobic submerged biofilm reactor for simultaneous carbon andnitrogen removal from the municipal wastewater is potential to avoid sludge settling problems in theconventional activated sludge.

Acknowledgements

This research was carried out and financed within the framework of the research activities of thePrince Khalid Bin Sultan Chair for Water Research, College of Engineering, King Saud University.

The authors would like to thank director and employee of Manfoha wwtp for their cooperation

The authors would like also to thank Mohamed Ikbal for his support during the follow up of the systemand lab analyses.

Future Plan

A project titled “Submerged Biofilm Reactor for Carbon and Nitrogen Removal from MunicipalSewage in Saudi Arabia”

has been approved by the NPST

Project Code: 13-ENV1070-02

The total budget: 1152925 SR including administration fees