Capturing organics from municipal wastewater using a primary sludge-derived polymer

Abstract

Among the numerous organics capture technologies, chemical enhanced primary treatment (CEPT) offers several distinct advantages, including low energy consumption, less oxidation of organic matter, and large-scale operation. However, CEPT currently relies heavily on metal salt-based coagulants, which have some limitations in terms of agent costs, sludge volume, and alkalinity variation. This preliminary study proposes the use of organic matter from municipal wastewater as raw materials (i.e., primary sludge) for the preparation of organic polymer, which would be used in place of conventional inorganic coagulants for organics recovery. An organic flocculant (PSBs-g-PAM-co-PDMC) was prepared by grafting DMC [(2-methacryloyloxyethyl) trimethyl ammonium chloride] and AM (acrylamide) onto the backbone of primary sludge-derived biopolymers (PSBs), which formed during the of sludge hydrothermal treatment. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential analysis, and gel permeation chromatography were used to characterize the chemical properties of PSBs-g-PAM-co-PDMC. These methods confirmed the incorporation of AM and DMC into the PSBs' backbone. PSBs-g-PAM-co-PDMC was used to investigate the COD (chemical oxygen demand) capture characteristics of real municipal wastewater. The results indicated that by dosing 30 mg/L PSBs-g-PAM-co-PDMC, approximately 60.0% of the COD was removed. At a low dosage (≤10 mg/L), COD can be efficiently reduced by removing predominantly particulate COD, while at a higher dosage, the further decrease of COD depends on the removal of colloidal COD. Both increasing and decreasing the pH have an effect on the COD removal mechanism. Additionally, the effluent quality and production cost were analyzed.