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ambient air temperature slow biological activity and thus degrade performance. Waterloo <br />Biofilter now uses rigid baskets or bulk filter tanks to avoid problematic slumping. <br />Total Suspended Solids (TSS) removal. <br />Total Suspended Solids (TSS) measured in the technology effluent averaged 6.2 mg/l <br />(median 4.0 mg/1) over the monitoring period, versus 160 mg/l for influent wastewater, <br />representing a removal rate of 96 per cent (Table 2). ). Measurements exceeded the <br />threshold 30 mg/l level less than 2% of the time (2 out of 118 samples taken). Standard <br />deviation, a reflection of the variability of the performance was relatively low, an <br />indication that the technology was able to provide good removal performance <br />consistently over the testing period. <br />Table 2. Total Suspended Solids (TSS) removal performance of the Waterloo Biofilter® <br />system during testing at the Massachusetts Alternative Septic System Test Center - June <br />1999- June 2001. <br />TSS (mg/1) <br />Replicate <br />1 <br />Replicate <br />2 <br />Replicate <br />3 <br />Influent <br />Mean <br />%Removal <br />Average <br />6.7 <br />6.1 <br />5.5 <br />160 <br />6.2 <br />96.2% <br />Median <br />3.5 <br />4.0 <br />3.0 <br />161 <br />Standard Deviation <br />6.6 <br />7.6 <br />6.7 <br />55 <br />Maximum <br />26.0 <br />46.0 <br />31.0 <br />323 <br />Minimum <br />0.0 <br />1.0 <br />0.0 <br />47 <br />Count <br />44 <br />45 <br />29 <br />44 <br />Count> 30 mg/1 <br />0 <br />1 <br />1 <br />44 <br />As with the BOD results above, the three maximum values occurred in May 2000 and the <br />causes were also basket slumping. When the baskets were repaired subsequent samples <br />show an improvement in the effluent quality (Figure 2) until the period January -April <br />2001 when levels rose to level of 20-21 mg/1. Again this decline in efficiency appears to <br />be a seasonal effect: lower influent wastewater temperature and ambient air temperature <br />slow biological activity and thus degrade performance. <br />Nitrogen removal <br />Total nitrogen (TN) measured in the technology effluent averaged 14.4 mg/1(median, <br />13.9 mg/1) over the monitoring period, versus 35.0 mg/1 for influent wastewater, <br />representing a removal rate of 59 per cent (Table 3). TN measurements exceeded the <br />threshold 19 mg/l level 13% of the time (16 out of 124 samples taken), principally in Unit <br />2. <br />Units 1&3 had very good nitrogen removal performance, 11.9 and 13.2 mg/l IN <br />respectively, with only one sample above 19 mg/1. While the performance of Unit 2 was <br />similar to Units 1&3 through the first 14 months of testing (Table 4), performance <br />Performance Results - WaterlooBiofilter® Page 7 of 28 <br />