Agricultural and non-agricultural directions of bio-based sewage sludge valorization by chemical conditioning

This literature review outlines the most important—agricultural and non-agricultural—types of sewage sludge management. The potential of waste sludge protein hydrolysates obtained by chemical sludge conditioning was reported. The discussed areas include acidic and alkaline hydrolysis, lime conditioning, polyelectrolyte dewatering and other supporting techniques such as ultrasounds, microwave or thermal methods. The legislative aspects related to the indication of the development method and admission to various applications based on specified criteria were discussed. Particular attention was devoted to the legally regulated content of toxic elements: cadmium, lead, nickel, mercury, chromium and microelements that may be toxic: copper and zinc. Various methods of extracting valuable proteins from sewage sludge have been proposed: chemical, physical and enzymatic. While developing the process concept, you need to consider extraction efficiency (time, temperature, humidity, pH), drainage efficiency of post-extraction residues and directions of their management. The final process optimization is crucial. Despite the development of assumptions for various technologies, excess sewage sludge remains a big problem for sewage treatment plants. The high costs of enzymatic hydrolysis, thermal hydrolysis and ultrasonic methods and the need for a neutralizing agent in acid solubilization limit the rapid implementation of these processes in industrial practice. Graphical abstract

Distribution Characteristics of Inorganic Solids in Biochemical Treatment System

This paper studies the accumulation mechanism of different types of inorganic solids in activated sludge system by taking two main kinds of inorganic solids-chemical sludge and sediment as the research object. In the chemical phosphorus removal experiment, self-made calcium silicate hydrate was used as the chemical phosphorus removal agent and added to the end of the biochemical system of domestic sewage for phosphorus removal experiment, while the fine sediment was simulated by quartz sand of 26, 73, 106, 165 and 210 μm respectively, and a complete mixture model of inorganic solid accumulation was established as Xiss = Ciss, inf × (SRT/HRT + 1) × (1 – e–t/SRT). The results showed that the self-made hydrated calcium silicate had good phosphorus removal effect, and the TP of domestic sewage could be removed from 7 mg/L to 0.5 mg/L. The chemical sludge accumulation in the phosphorus removal process conforms to the complete mixing model, and the relative errors of measured and predicted values of MLVSS/MLSS and MLISS were 1% and 3%, respec- tively. The sediment accumulation process does not conform to the completely mixed model. The relative error of MLVSS/MLSS is between 56% and 77%, and that of MLISS is between –45% and –80%. The accumulation forms of inorganic solids in different forms of activated sludge systems are also different. Chemical sludge is mainly suspended in the mixture, reducing the proportion of MLVSS/MLSS. In activated sludge system, sediment is accumulated in various forms such as suspension and deposition.

RAVITA Technology – new innovation for combined phosphorus and nitrogen recovery

Present phosphorus (P) recovery technologies mainly contain P recovery from sludge liquor or ash. These types of technologies are suitable for large wastewater treatment plants (WWTPs) with enhanced biological phosphorus removal (EBPR), digestion and/or incineration. In Finland and other Nordic countries, strict P discharge limits require chemical precipitation, thus EBPR alone is not sufficient. Ammonium recovery from wastewater, on the other hand, is not so often discussed. However, recovery from WWTP reject waters would decrease the energy demand of ammonium synthesis by Haber-Bosh technology and the energy demand of the WWTP's biological process. Helsinki Region Environmental Services Authority (HSY) has developed a new process called RAVITA whereby P and nitrogen recovery are combined in order to produce phosphoric acid (H3PO4) and ammonium phosphate (NH4)3PO4. Furthermore, in this process metal salt used in precipitation is recovered. The research was carried out on pilot (1,000 population equivalent) and laboratory scales. The objectives of this article are to explain the principles of the RAVITA process and give the first results of processing and production of chemical sludge.