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Evaluation of a pilot constructed wetland system as an appropriate technology for septage treatment in Cambodia Chiew, Hannah


Septic tanks are one of the most commonly used forms of onsite sanitation systems in developing countries. However, lack of regulation on the design and installation and the lack of proper disposal for the septage generated may cause serious environmental degradation and pose serious public health hazards. This study presents the findings of a pilot-scale constructed wetland system in Cambodia for the treatment of septage for 8 months. After a 6-month Acclimatization Period, the system was operated at two hydraulic loading rates (HLRs) of 15.5 and 27.4 mm/day to evaluate the impact of HLR on the treatment efficacy. During the 8-month period, the system achieved mass removal efficiency of 96% - 98% for total suspended solids (TSS), 80% - 97% for turbidity, 61% - 78% for biological oxygen demand (BOD) and 61% - 90% for chemical oxygen demand (COD), but was less efficient in removing total phosphorus (TP) and total nitrogen (TN), which exhibited efficiencies of 52% - 58% and 57% - 66%, respectively. The system also achieved 1.56 – 2.25 log reduction for E. coli and 0.49 – 0.81 log reduction for total coliform (TC). Although the HLR was almost doubled during the 2-month period, the effluent quality did not degrade appreciably in most cases, and caused little or no impact on the treatment efficacy. It is possible that harvesting prior to the start of the HLR exercise had an adverse impact on the eco system and de-stabilized the system, causing the results with lower HLR (or higher HRT) to be worse than expected. Another possible reason for the lack of difference could be due to the high variability of influent quality. It is possible that there is no apparent benefit in decreasing the HLR in this case. The k-C* , or first order removal model, was used to model the longitudinal concentration profile and estimated the removal rate constant. There were no apparent relationships between HLR and the removal rate constants in the k-C* model. The effluent may be suitable for localized and restricted irrigation with careful crop selection, or re-used with dilution due to its high nitrogen content.

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