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Pre-concentration of municipal wastewater by chemically enhanced primary treatment (CEPT) was studied under controlled laboratory conditions. Both iron and aluminium-based coagulants were examined at gradually increasing concentrations (0.23, 0.35, 0.70 and 1.05 mmol/L). The CEPT sludge generated from different coagulation experiments was digested in batch anaerobic reactors, while the supernatant was tested in a dead-end microfiltration setup. The results of the study show that biogas yield was dramatically decreased (from 0.40 to 0.10 m(3)/kg chemical oxygen demand of influent) with increasing coagulant dose. In contrast, supernatant filterability was improved. Based on the laboratory results, a conceptual design was produced for a community of 2000 inhabitant equivalents (IE), using CEPT technology (at low coagulant dose) with anaerobic digestion of the concentrates. According to this, the capital and operational costs were 0.11 and 0.09 €/m(3), respectively. The biogas generated is used for digester heating and the overall process is energy self-sufficient. At a small-scale and in private applications, CEPT technology is preferably operated at higher coagulant dose, followed by membrane filtration for water reuse. Accordingly, sewage purification and reuse is possible without implementing aerobic biological processes.

Energy autarky of sewage treatment plants, while reaching chemical oxygen demand (COD) and N discharge limits, can be achieved by means of shortcut N-removal. This study presents the results of a shortcut N-removal pilot, located at the biological two-'stage (high/low rate) wastewater treatment plant of Breda, The Netherlands. The pilot treated real effluent of a high-rate activated sludge (COD/N = 3), fed in a continuous mode at realistic loading rates (90-100 g N/(m(3)·d)). The operational strategy, which included increased stress on the sludge settling velocity, showed development of a semi-granular sludge, with average particle size of 280 μm (ø(4,3)), resulting in increased suppression of nitrite-oxidizing bacteria. The process was able to remove part of the nitrogen (51 ± 23%) over nitrite, with COD/N removal ratios of 3.2 ± 0.9. The latter are lower than the current operation of the full-scale B-stage in Breda (6.8-9.4), showing promising results for carbon-efficient N-removal, while producing a well settling sludge (SVI(30) < 100 mL/g).

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Unique pilot design and innovative control strategies enabled mainstream nitrogen removal with a low COD to N removal ratio at both summer and winter conditions.