Molecular dynamic modeling of EPS and inorganic/organic flocculants during sludge dual conditioning

Interaction of poly dimethyl diallyl ammonium chloride with sludge components: Anaerobic digestion performance and adaptive changes of anaerobic microbes

The wide utilization of poly dimethyl diallyl ammonium chloride (polyDADMAC) in industrial conditions leads to its accumulation in waste activated sludge (WAS), thereby affecting subsequent WAS treatment processes. This work investigated the interaction between polyDADMAC and WAS components from the perspective of anaerobic digestion (AD) performance and anaerobes adaptability variation. The results showed that polyDADMAC decreased the content of biodegradable organic substrates (i.e., soluble protein and carbohydrate) by binding with the functional groups and then settling to the solid phase, thus impeding the subsequent utilization. Higher concentrations of polyDADMAC prompted an initial protective response of excreting organic substrates into extracellular environment, but its toxicity to archaea was irreversible. Consequently, polyDADMAC inhibited the processes of AD and induced a 30 % reduction in methane production with 0.05 g polyDADMAC/g total suspended solid (TSS) addition. Changes in microbial community structure indicated that archaea involved in methane production (e.g., Anaerolineaceae sp. and Methanosaeta sp.) were inhibited when exposed to polyDADMAC. However, several adaptive bacteria with the ability of utilizing complex organics and participating in nitrogen cycle (e.g., Aminicenantales sp. and Ellin6067 sp.) were enriched with the above dosage. Specifically, the decreased abundance of genes relevant to methane metabolism pathway (i.e., mer and cdh) and increased abundance of genes involved in metabolism of cofactors and vitamins (e.g., nad and thi) indicated the toxicity of polyDADMAC and the irritant response of microflora. Moreover, polyDADMAC underwent degradation in AD system, resulting in a 12 % reduction in 15 days, accompanied by an increase in the -NO2 functional group. In general, this study provided a thorough understanding of the interaction between polyDADMAC and WAS components, raising concerns regarding the elimination of endogenous pollutants during AD.

Low-cost optimization of industrial textile landfill sludge re-dewatering using ferrous sulfate and blast furnace slag

This study was based on an industrial sludge landfill with a scale of 1 million cubic meters, which had been filled for more than 10 years. It focused on the secondary dewatering of industrial textile landfill sludge (LS) with a total organic carbon (TOC) content greater than 50% and a volatile suspended solids to suspended solids (VSS/SS) ratio of 0.59. A response surface methodology (RSM) model was established using the coagulant ferrous sulfate (FeSO4) and conditioning agents such as hydrated magnesium oxide (MgO), blast furnace slag (BFS), and calcium oxide (CaO). By solving the RSM equations for the respective indicators, the optimal dosages of FeSO4, MgO, and BFS were determined to be 90 mg/g of dry sludge (DS), and for CaO 174.85 mg/g DS. Further examinations of the dewatering performance, apparent properties, extracellular polymeric substances (EPS) components, rheological characteristics, moisture distribution, and pollutant content variation led to the development of a green waste-based dewatering agent composed of FeSO4 and BFS. In small-scale diaphragm plate and frame filter press tests, the optimal water content (WC) was 69.11%. In the final production-scale experiments, it was 65.72%, with the actual application cost being only 13.07 $/ton DS. Additionally, when FeSO4 and BFS were used together, the combined action of Fe and Si could significantly reduce the biotoxicity of heavy metals (HMs), cut down 75.2% of the LS's TOC, and effectively reduced the leaching of organic substances from the leachate, which was beneficial for subsequent disposal. In conclusion, the combined use of FeSO4 and BFS for the secondary dewatering of industrial textile LS was economically efficient, effective in dewatering, and had significant harm reduction effects, making it a worthwhile for waste treatment.

Quaternization-based graft modification of straw fibers for conditioning the sludge dewatering performance

Extracellular polymeric substances (EPS) are a critical influencing factor in sludge dewatering. Disrupting such EPS contributes to the release of bound water in sludge, enhancing the sludge dewatering performance. In This study, quaternized straw fibers that are destructive to the EPS structure and components in active sludge were prepared useing heterogeneous free radical graft polymerization. Straw fibers, dimethyl diallyl ammonium chloride (DMDAAC), ammonium persulfate (APS), and acrylamide (AM) were taken as the substrate, grafting monomer, catalyst, and cross-linking agent, respectively.The optimal processing conditions determined for the DMDAAC-based quaternization and graft modification of straw fibers were as follows: reaction temperature of 60 °C, reaction time of 5 h, 0.100 g of catalyst APS dosage per gram of straw, and 3.000 ml of DMDAAC dosage per gram of straw. The optimal processing conditions yielded 1.335 g of modified straw fibers per gram of straw, 33.67% grafting rate, and 31.70% substitution of the quaternary ammonium groups. The capillary suction time (CST) was conditioned from 243.3 ± 22.6 s in the original sludge to 134.5 ± 34.45 s. The specific resistance to filtration (SRF) was reduced from 8.82 ± 0.51 × 1012 m/kg in the original sludge to 4.59 ± 0.23 × 1012 m/kg.

Effects of chitosan and rice husk powder on thermal hydrolysis-anaerobic digested sludge conditioning: Dewaterability and biogas slurry fertility

To enhance the dewaterability of anaerobic digested sludge and to make full use of the biogas slurry. This study set up five sludge conditioning methods: polymeric ferric sulfate, polymeric aluminum chloride, cationic polyacrylamide, chitosan, and chitosan combined with rice husk powder. Their effects on the dewaterability of thermal hydrolysis-anaerobic digested sludge, bacterial community, and biogas slurry fertility were studied to find a non-toxic and non-risk dewatering technology for the environment and biogas slurry. Compared with that of the control group, moisture content, normalization capillary suction time, and specific resistance to filtration were reduced by 12.8%, 97.7%, and 82.9%, respectively. Chitosan enlarges the sludge flocs and forms complexes with proteins, disrupting the structure of the extracellular polymeric substances, thereby exposing more hydrophobic groups and reducing the hydrophilicity of the sludge. The subsequent addition of rice husk powder enhances the adsorption of hydrophilic substances and provides a stronger drainage channel for the sludge. In addition, the biogas slurry obtained by this conditioning method used as a fertilizer increased the dry weight and fresh weight of corn seedlings by 59.3% and 91.0%, respectively. And the total chlorophyll content increased by 84.6%. Pearson's correlation analysis showed that chitosan and rice husk meal had no toxic effect on the biogas slurry compared to the other three flocculants. The results showed that the combined treatment of chitosan and rice husk powder resulted in the best dewaterability. Overall, chitosan combined with rice husk powder is a green dewatering technology with great potential for anaerobic digested sludge dewatering and biogas slurry recycling.