Technologies for Wastewater and Sludge Treatment

Challenges associated with mesophilic digestate (MD) involve volume, odor, and pathogens, which effective post-digestion treatments can address. The efficiency of MD post-treatment can be enhanced by conditioning with ferric chloride (FeCl₃), hydrogen peroxide (H₂O₂), and polymer. This study aimed to observe the effect of combined chemical conditioning on volume reduction, phosphorus (P) release, odor, and pathogen reduction potential for MD. MD was conditioned with polymer only, polymer and FeCl₃ at pH adjusted to 8.0 with lime (Ca(OH)₂), and a blend of polymer, FeCl₃, and hydrogen peroxide (H₂O₂) at pH 8.0. The results show that adding all three chemicals improved post-treatment efficiency at 2.1 kg/t DS FeCl₃, 2.1 kg/t DS polymer, and 600 mg/L H₂O₂ at pH 8.0, compared with polymer or dual conditioning. At the combined dose, cake solid content, centrate P removal, and odor reduction capability improved compared with raw MD by 20%, 99%, and 66%, respectively. Combined chemical treatment reduced fecal coliform by 98% but does not fulfil class A requirements and showed 50% regrowth potential. The synergic effect of polymer, FeCl₃, H₂O₂, and alkaline pH breakdown EPS, reduced water holding capacity and formed compacted flocs for better water removal and settling. This combination also precipitated P through FeCl₃ while H₂O₂ oxidation curbs odor, enhancing further P removal from centrate. Full article

In line with the strategy of transforming existing municipal wastewater treatment plants (WWTP) from disposal facilities into systems for using domestic wastewater (WW) as a source of energy and raw materials, a concept consisting of chemical, physical, and biological steps has been set up as a pilot project in WWTP Büsnau, Stuttgart, Germany. The key part of the entire process is based on the use of advanced microsieving (MS) to eliminate remaining particulate organic carbon (POC) (mg/L) from the effluent of the primary sedimentation tank (PST). Therefore, in the primary stages of this project, it was necessary to have a broad vision and a true understanding of the particle size distribution (PSD) of municipal WW. As a novel approach, in the present study, the conventional PSD method was optimized by implementing certain modifications, and the tests were conducted in situ. The modified PSD analyses facilitated in-depth investigations of solid–liquid separation at WWTPs and showed that drying samples in the oven can result in a 20% to 30% deviation in the POC (mg/L) removal results. In addition, the idea of the substitution of PSTs with an MS was supported by the results of this study. It was determined that an MS with a pore size of 45 µm to 63 µm can provide the same elimination efficiency as a PST. Another significant outcome of this study was the introduction of suitable mesh sizes for the MS which were coupled with PST in order to extract the maximum amount of POC (mg/L) from the municipal WWTPs without the addition of any chemicals. The results revealed that up to 90% of the TSS (mg/L) and 70% of the COD (mg/L) can be removed if an MS with a mesh size between 4 µm and 20 µm is coupled with a PST. Full article

Municipal sludge biochar (MSBC) can be used to absorb phosphorus in water for waste treatment. Nano-zero-valent zinc (nZVZ) was uniformly attached to MSBC to obtain a highly efficient phosphorus-absorbing composite material, nZVZ–MSBC. Characterization by FTIR, XPS, XRD, and BET showed that nZVZ was uniformly dispersed on the surface of the MSBC. Zinc loading was able to greatly improve the adsorption performance of MSBC for phosphorus. Adsorption experiments illustrated that the adsorption process conformed to the Langmuir model, and the maximum adsorption amount was 186.5 mg/g, which is much higher than that for other municipal sludge biochars. The adsorption process reached 80% of the maximum adsorption capacity at 90 min, and this gradually stabilized after 240 min; adsorption equilibrium was reached within 24 h. The optimum pH for adsorption was 5. The main adsorption mechanism was chemical adsorption, but physical adsorption, external diffusion, internal diffusion, and surface adsorption also played roles. The potential for application as an efficient adsorbent of phosphorus from water was confirmed. In addition, a novel strategy for municipal sludge disposal and resource utilization is provided. Full article