Disinfection Using Biosand Filter Two lab scale Biosand filters were constructed using sand and gravel available in Civil Engineering materials laboratory of University of Nizwa as per the specifications of Abhilash Nair et al..[56]. The first filters had a 5 cm under drain gravel and 15 cm of sand layer (Figure 1). The first filters had a 5 cm under drain gravel and 10 cm of sand layer (Figure 1).

Figure 1. Biosand filters used in the studyWorking mechanism Figure 2 shows the components of the Biosand filter. To use a Biosand filter, initially pours raw water poured into the reservoir above uniformly and the water moves through the filter by gravity. The raw water should be poured slowly to prevent it from disturbing the biological layer (also known as the schmutzdecke) in the top few centimeters of sand. It is believed that most removals of microbes and particles occur in the upper biological layer (CAWST, 2008; Unger and Collins, 2008) and filter performance improves over time as the filter ripens (Ahammed, 2011; Stauber, 2007). The influent water displaces the water in the filter, was collected by a drain system at the bottom of the filter and removed via a vertical tube whose outlet is a few centimeters above the surface of the sand. This allows a standing layer of water to remain above the top of the sand, which keeps the media saturated, prevents it from drying out, and preserves the microbial community. After a charge of water has been put into the filter, the filter must remain idle for some time, usually 6 to 12 hours. This allows the microbes to complete the degradation of contaminants (CAWST, 2008).

Figure 2. Schematic of Biosand filterEfficiency of Biosand filter in disinfecting Falaj waterTo know the efficiency of Biosand filter in removing pathogen bacteria present in the falaj water, falaj water has been put into the filter, the filter kept remain idle for 12 hours. This allows the microbes to complete the degradation of contaminants (CAWST, 2008). After 12 hours of idle flooding, effluent was collected from the under drain at different time intervals. Microbial concentration in the effluent collected from two bio-filters at different time intervals is presented in table 1 and graphically represented in figure 3.

Table: 1 Efficiency of bio sand filter in disinfecting falaj waterTime since start of the experiment (hr)Depth of The Filter= 10 cmDepth of The Filter= 15 cm

InitialFinal% RemovalInitialFinal% Removal

24609560860952015

486095001860946024

726094502660940034

966093524260932047

1206093025060924061

1446092535960919069

1686091986760916074

1926091966860914177

2166091956860913977

2406091956860913878

Figure 3 . Efficiency of bio-filter in treating Falaj waterFrom figure 3 it was observed that percentage removal of pathogen organisms depends on time since start of the experiment ie sample collection time and depth of the filter. As depth of the filter and time of sampling increased percentage removal increased. It is believed that most removals of microbes and particles occur in the upper biological layer (CAWST, 2008; Unger and Collins, 2008) and filter performance improves over time as the filter ripens (Ahammed, 2011; Stauber, 2007).Death and predation are mainly responsible for the removal of pathogenic bacteria. The bacteria are preyed upon by the organism colonised in biological layer developed over the top of filtering media called as Schmutzdecke layer (Buzuniz 1995). The pathogens also starve due to lack of food in the filter as the organic matter in the influent water is trapped on the top layer and consumed by the microbes colonised in Schmutzdecke (Buzuniz 1995).

Efficiency of Biosand filter in disinfecting treated effluentTo know the efficiency of Biosand filter in removing pathogen bacteria present in the treated effluent, treated effluent has been put into the filter, the filter kept remain idle for 12 hours. This allows the microbes to complete the degradation of contaminants (CAWST, 2008). After 12 hours of idle flooding, effluent was collected from the under drain at different time intervals. Microbial concentration in the effluent collected from two bio-filters at different time intervals is presented in table 1 and graphically represented in figure 4.Table: 2 Efficiency of bio sand filter in disinfecting treated effluentTime since start of the experiment (hr)Depth of The Filter= 10 cmDepth of The Filter= 15 cm

InitialFinal% RemovalInitialFinal% Removal

24101290011101284517

48101284517101278023

72101278922101265236

96101265036101257044

120101257643101249851

144101250250101242258

168101243457101236065

192101240360101230070

216101240061101229871

240101239861101229671

Figure 4 . Efficiency of bio-filter in treating Falaj waterFrom figure 4 it was observed that percentage removal of pathogen organisms depends on time since start of the experiment ie sample collection time and depth of the filter. As depth of the filter and time of sampling increased percentage removal increased. It is believed that most removals of microbes and particles occur in the upper biological layer (CAWST, 2008; Unger and Collins, 2008) and filter performance improves over time as the filter ripens (Ahammed, 2011; Stauber, 2007).Death and predation are mainly responsible for the removal of pathogenic bacteria. The bacteria are preyed upon by the organism colonised in biological layer developed over the top of filtering media called as Schmutzdecke layer (Buzuniz 1995). The pathogens also starve due to lack of food in the filter as the organic matter in the influent water is trapped on the top layer and consumed by the microbes colonised in Schmutzdecke (Buzuniz 1995).