Effect evaluation of anoxic-anaerobic-oxic household latrine

Objective To evaluate the sewage treatment effects of household anoxic-anaerobic-oxic (AAO) latrine.

Methods Sixty rural household AAO latrines in Shandong Province were randomly selected. Influent and effluent wastewater samples from the septic tank of each latrine were collected to test the chemical oxygen demand (CODcr), total nitrogen (TN), ammonia nitrogen (NH₃-N), colority, total phosphorus (TP), pH and fecal coliform group (FC).

Results In effluent tanks, the concentrations of CODcr, TN, NH₃-N and TP, as well as the colority and pH vaule in median(P₂₅, P₇₅) were 405.00(180.50, 585.25) mg/L, 193.50(69.00, 603.00) mg/L, 176.00(80.50, 368.75) mg/L, 11.00(6.00, 16.00) mg/L, 162.00(0.50, 748.00) TCU and 7.75(7.32, 8.04), respectively. The Wilcoxon rank sum test showed that all indicators except pH were significantly lower in effluent samples than in influent samples (P<0.05). The qualification rates of CODcr, TN, NH₃-N, colority, TP, pH and FC in effluent samples were 56.67%(34/60), 28.33%(17/60), 25.00%(15/60), 40.00%(24/60), 28.33%(17/60), 85.00%(51/60), and 50.00%(30/60), respectively. The mean removal rates of CODcr, TN, NH₃-N, colority, TP and FC were 56.17%, 47.12%, 44.84%, 62.19%, 62.53% and 72.36%, respectively. Logistic regression analysis showed that the household latrines of no sewage discharging into the septic tankOR=3.999, 95%CI: (0.804, 19.883) and the 2-year running time household latrine had higher harmless effect qualification rates than those of 3 and 4 yearsOR values were 2.464 and 1.507, and 95% CI were(1.015, 4.742) and (1.093, 1.919), respectively.

Conclusion AAO toilets show good performance in treating FC, CODcr and colority in rural mixed sewage, but poor on TN, NH₃-N and TP.