4. RESULTS AND DISCUSSIONS
4.2. Characterization Test Results
74
4. RESULTS AND DISCUSSIONS
75 Tot C: Total Carbon
Tot N: Total Nitrogen RI7: Respiration Index
4.2.2. Eluate
Table 4.2-2: Characterization of the Eluate after 24 hours
pH
The results in Table 4.2-2 shows that the pH in all the substrates that were used is closer to neutrality. This pH level is more favorable on the rate of nitrate removal as the optimum pH required for the biological denitrification range between 6 and 8 (Plug et al 2010). It could be observed that the composting of the solid waste has produced a favorable pH for the denitrification compared to other research results done by Plug (2009) where CGRraw , CGR10
only were used-their pH was low as 5.45 (Plug, 2009). Low pH could negatively affect the rate of nitrate removal as discussed in section 2.7.2.1.
Ammonia-N
The results presented in Table 4.2-2 shows a high level of NH3-N present in all the substrates especially Cell 2 which may cause the NH3-N to leach from the substrate into the wastewater being treated, thereby causing an increase in nitrate level through a process known as bioleaching. In the event of sufficient oxygen in the bioreactor the NH3 that has leached out of the substrate could be converted from NH3 to NO2 thereby increasing the NO2present, therefore lowering the nitrate removal efficiencies within the reactor.
Total Nitrogen and Total Carbon
The carbon-to-nitrogen ratio affects the decomposition because organisms use carbon as a source of energy. A higher carbon content than nitrogen content within a substrate was necessary for denitrification to occur. Correct proportion of carbon is required for energy and
Cell 1 11.69 ± 2.41 2.84 ± 0.28 7.20 1437.26 ± 73.69 21.50 2.10 0.35 1.69 0.07 24.14
Cell 1 + CGRraw 8.14 ± 0.15 4.99 ± 0.78 7.03 3298.60 ± 818.52 137.00 0.70 0.70 1.69 0.04 42.25
Cell 1 + CGR10 15.52 ± 0.4 8.47 ± 0.40 7.47 4323.94 ± 815.28 148.00 1.40 1.12 0.82 0.04 20.50
Cell 2 10.6 ± 0.17 4.77 ± 0.63 7.23 3328.45 ± 186.93 39.17 11.55 12.60 0.71 0.03 23.67
Cell 2 + CGRraw 8.3 ± 0.85 3.61 ± 0.34 7.03 3249.98 ± 244.51 108.97 11.20 12.60 0.83 0.04 20.75
Cell 2 + CGR10 11.48 ± 0.20 4.98 ± 0.15 7.18 4136.24 ± 487.48 127.97 16.80 15.40 0.62 0.03 20.67
CGRraw 5.83 ± 0.19 4.17 ± 0.65 7.47 3471.48 ± 1720.33 14.00 6.10 0.58 0.02 29.00
CGR10 7.17 ± 0.42 4.96 ± 0.58 7.47 3876.23 ± 370.33 <1 <1 0.63 0.05 12.60
BOD (mg/l)
Sample TS (%) VS (%) pH COD (mg/l) NH3 (mg/l) NOx (mg/l) Tot C (%) Tot N (%) C:N Ratio
76
nitrogen for the production of protein (Composting101, 2006). Cell 1 + CGRraw was found to have the highest C/N ratio which indicate that Cell 1 + CGRraw is the most suitable carbon source when compared to the other substrates used-that is: Cell 1, Cell 2, Cell 1 + CGR10, Cell 2 + CGR10 and Cell 2 + CGRraw. According to Wu et al (2002) citied by Tsui et al, (2007) the typical range for stabilized composted waste is between13-16. It could be observed from Table 4.2-1 that Cell 1 + CGRrawand Cell 2 falls above the range while Cell 2 + CGR10fall below that range. Cell 1 + CGRrawand Cell 2 should be the appropriate for denitrification as more carbon is required than nitrogen.
Cell 2 + CGR10 has the lowest C/N ratio compared to the other substrate of 12.22.This could be due to the less carbon and more nitrogen which could cause it to achieve the lowest denitrification efficiencies in comparing to the other substrates. However C/N ratio is not the only factor that is used to determine the suitability of the substrate as stated in section 2.7.2.1.
Cell 1 + CGR10have the highest COD of 4324 mg/ℓ while it has a BOD5 of 127.97 mg/ℓ as presented in Table 4.2-2. This suggests that despite the high COD only a small portion is readily available for the biological denitrification of nitrates hence the effluent will requirefurther treatment prior to discharge. The substrate with low BOD5 : COD ratio as indicated in Table 4.2-2 suggest that the substrate has been extensively biodegraded
Figure 4.2-1: RI7 of Solid Substrates
0.00 20.00 40.00 60.00 80.00 100.00 120.00
Cell 1 (8 wks)
Cell 2 (16 wks)
Cell 1 + CGRraw
Cell 2 + CGRraw
Cell 1 + CGR10
Cell 2 + CGR10
CGRRAW CGR10
RI7 2.60 1.77 19.33 18.25 15.21 11.14 110.34 44.11
RI7 (mg 02 /g DM )
Respiration Index of Solid Substrates at 7 days (RI7)
RI7
77 RI7
The respiration Index (RI7) test as stated in section 3.4.3 is used to determine the biodegradability of each substrate including it stability level. Figure 4.2-1 suggests that CGRraw
has a higher RI7 compared to the other substrates which is expected since CGRraw consist of fresh commercial garden refuse.The high RI7of CGRraw indicates that it has notdegraded, therefore it is unstable. As expected the Cell 2‟s substrates have a lower RI7 (Figure 4.2-1) compared to Cell 1 and Cell 1 mixtures.This shows that while composting process was taking place the Cell 2 has become more stable and maturedthan the Cell 1‟s substrates. It could be observed that Cell 1 state has high biodegradable material compared to Cell 2 and Cell 2 mixtures. The Cell 2 and Cell 2 mixture is slowly biodegrading because it is more stable than Cell 1 and Cell 1 mixtures. As suggested by Trois et al (2010), a lower RI7 values suggests high level of stability in the compost to maintain denitrification.
4.2.3. Leachate
The leachate (Treated and Untreated-Mixed liquor) was collected from the SBR treatment plant at Mariannhill landfill site. Before any experiments were conducted the quality of the leachate was measured (Characterization of leachate) and the summary result of the initial quality of the leachate used is shows in Table 4.2-3.
Table 4.2-3: Results of input Leachate Quality
Treated Leachate 500 1.55 ± 0.032 0.25 ± 0.024 7.40 203 40.9 ± 4.58 7.70 27.30 0.54 0.05 10.8 Seeded Treated Leachate 500 1.62 ± 0.02 0.28 ± 0.026 7.73 206 45.17 ± 17.64 9.10 44.10 0.75 0.02 37.5 Mixed liquor 2500 13.42 ± 0.26 4.93 ± 0.23 7.11 5406 105.93 ± 4.98 11.90 4.90 0.54 0.06 9.00 NH3 (mg/l) NOx (mg/l) Tot C (%) Tot N (%) C:N Ratio COD (mg/l) BOD (mg/l)
NO3 (mg/l)
Sample TS (%) VS (%) pH
From Table 4.2-3, it is observed that the leachate is characterised by low level of ammonia except the mixed liquor leachate as it was sampled from the SBR tank where the raw leachate is treated for ammonia. The BOD5 level was also low except the mixed liquor. However the nitrate level in the treated leachate is high. This is because the leachate in the SBR is treated for ammonia which is then converted to nitrate: and hence is the need for this research.