Study of the process of mechanical dewatering of liquid waste from municipal wastewater treatment plants in sedimentation centrifuges

Abstract

The article presents the results of studies of the process of mechanical dewatering of liquid waste from municipal wastewater treatment plants in Kharkiv, in particular, sediments formed at all stages of biological wastewater treatment. The city's wastewater has excessive concentrations of suspended solids (up to 400 mg/dm³), biochemical oxygen demand (up to 250 mg/dm³) and low transparency (1.9 cm), which complicates effective mechanical treatment. The paper analyses the operation of the main mechanical treatment facilities, including sand traps, primary and secondary settling tanks, as well as the sludge dewatering system, which includes a hydrocyclone GC-350 and an Ecomash SHS 511A-113 centrifuge. Industrial tests of the Dewatering Module have shown that continuous operation for 4-8 hours effectively removes coarse inclusions (stones, seeds, plant residues), and the concentration of suspended solids in the sludge is reduced during pretreatment. Laboratory studies have shown that conventional flocculation does not ensure proper deposition of activated sludge due to the presence of hydrophobic fat particles that cause flocs to float. A method of preliminary physical and chemical treatment with the addition of mineral carriers (clay, sand, anthracite) was proposed, which allows for dense, stable flocs that settle well. At the optimal dose of flocculant (0.06-3 kg/t) and dilution of sludge, an improvement in the deposition and quality of the fugate was observed. It is shown that the use of a model suspension with a carrier mineral and an optimal dose of flocculant allows achieving stable phase separation and reducing the moisture content of the sludge. The research results are useful for optimising the operation of wastewater treatment plants, increasing the efficiency of mechanical dewatering of sludge and reducing the volume of sludge masses for disposal or further processing.