The anaerobic process for the treatment of municipal and industrial wastewater has been in practice for over a century. Apart from treatment of wastewater, the process has the advantage of lower sludge and biogas production that can save energy. Application of this process in a primary clarifier in such a way that there is simultaneous digestion of primary settled sludge and organic removal from wastewater can be more advantageous in an aerobic treatment plant. The paper discusses the performance of such a primary claridigester at ambient temperature. With a single hydraulic retention time (HRT) of 4.5 h, the organic (chemical oxygen demand (COD) and biochemical oxygen demand (BOD)) removal efficiency was 36.3% and 34.6%, respectively. The biosolid production rate was 0.383 g VSS/g COD removed or 0.818 g VSS/g BOD3 removed. However, biogas contains 80.8% methane and the COD mass balance revealed the loss of removed COD as 41.5% in the form of dissolved effluent from the claridigester. On account of sludge characterization, it was observed that nitrogen and zinc were present in highest concentration (2.55% and 1,776 mg/kg dry solids) and other nutrient and heavy metal parameters were within limits of not posing any risk of soil toxicity if disposed of for enrichment of soil.

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