Zhongquan Wang

With the simultaneous increase in wastewater generation and wastewater treatment rates in China, the annual production of residual sewage sludge (RSS) has been steadily rising, exceeding 70 million tons with an 80% moisture content. The sustainable resource utilization of RSS will be the predominant disposal method instead of sanitary landfilling in China. This review aimed to systematically analyze the major sustainable resource utilization technologies for RSS. Firstly, the basic characteristics of RSS in China were analyzed. A comparative analysis was conducted to assess the advantages, disadvantages, and applicability of three primary sustainable resource utilization technologies for RSS: building materials, energy utilization, and phosphorus recovery, aiming to provide clear insights for the development of future strategies. The research findings revealed that no single method can economically and environmentally address all challenges in the utilization of RSS resources. It is necessary to adopt appropriate resource utilization technologies according to the characteristics of RSS from wastewater treatment, achieving integration of pollution control and resource utilization. This review can provide scientific guidance for future sustainable utilization of RSS resources.

An improved catalytic wet oxidation method for the disposal of excess activated sludge from a coal chemical wastewater treatment process by using the prepared Cu-Ce/γ-Al₂O₃ catalyst was reported. The effects of catalyst dosage, reaction temperature and time, and initial oxygen pressure on the degradation of the sludge were investigated. The maximum removal rate of volatile suspended solids, 93.2%, was achieved at 260 °C for 60 min with the catalyst 7.0 g·L⁻¹ and initial oxygen pressure 1.0 MPa. The removal rate of chemical oxygen demand was 78.3% under the same conditions. The production of volatile fatty acids, including mainly acetic acid, propanoic acid, and isobutyric acid, increased with the increasing temperature. These acids have the potential to be carbon sources for the biological treatment of wastewater. Scanning electron microscopy images showed that the sludge became a loose porous structure, which is beneficial for dewatering performance. The results of an energy dispersive spectroscopy analysis illustrated that the carbon element in the sludge substantially migrated from solid to liquid phases. Therefore, these results demonstrated that the proposed catalytic wet oxidation method offers a promising pathway for the disposal and utilization of excess activated sludge from the coal chemical wastewater treatment process.

Excess activated sludge produced from coal chemical industries has gained much attention, because of the huge volume and high hazardous risk of the sludge. The wet oxidation of coal chemical sludge was studied in this study by using a stainless steel batch reactor. The effects of reaction parameters, including the moisture content, the additional dose of sludge, reaction temperature and the additional amount of oxygen, were discussed. The results showed that the highest removal ratios of COD and TS could reach up to 72.3% and 56.4% respectively with moisture content of sludge 93%, initial oxygen pressure 1.7 MPa under 240°C for 60 min. The mass transfer processes of sludge and oxygen, and the reaction temperature, are very important parameters for the treatment. It was suggested that wet oxidation technology provides a suitable alternative method for the treatment of excess sludge from coal chemical industries.