Development of a sustainable treatment technology for domestic sewage

We propose an integrated chemical-physical-biological treatment concept for the low-cost treatment of domestic wastewater. Domestic wastewater was subjected to a chemically enhanced primary sedimentation (CEPS), followed by treatment in an upflow anaerobic sludge blanket (UASB) reactor. In addition, a regenerable zeolite was used to remove NH4+, either after CEPS pretreatment or after biological treatment in the UASB reactor. The CEPS pretreatment consisted of the addition of a coagulant (FeCl3) and an anionic organic flocculant and removed on average 73% of the total chemical oxygen demand (CODt), 85% of the total suspended solids, and 80% of PO4(3-) present in the wastewater. The UASB system, which consequently received a low CODt input of approximately 140 mg/L, was operated using a volumetric loading rate of 0.4 g CODt/L.d (hydraulic retention time [HRT] = 10 h) and 0.7 g CODt/L.d (HRT = 5 h). For these conditions, the system removed about 55% of the CODt in its influent, thus producing an effluent with a low CODt of approximately 50 mg/L. The zeolite, when applied in batch mode before the UASB reactor, removed approximately 45% of the NH4+, whereas its application as a post-treatment cartridge resulted in almost 100% NH4+ removal. The simple design and relatively low operating costs, due to low costs of added chemicals and low energy input (estimated at Euro 0.07-0.1 per m3 wastewater treated), combined with excellent treatment performance, suggest that this system can be used as a novel domestic wastewater treatment system for developing countries. Therefore, the system is called a Low-cost, Integrated Sewage Treatment (LIST) system.