Effects of Salinity on Expression Dewatering of Waste Activated Sludge

Co-treatment of municipal solid waste incineration fly ash (MSWI FA) and municipal sludge: A innovative method to improve sludge dewatering with fly ash dechlorination

The complexity of municipal sludge dewatering is a bottleneck problem limiting resource utilization. In this paper, adding municipal solid waste incineration fly ash (MSWI FA) to municipal sludge for enhanced dewatering was applied, while the chlorine salt in MSWI FA was simultaneously removed using water in municipal sludge. The effects of different dosages and chemical components of MSWI FA on municipal sludge dewatering, and the removal effect of municipal sludge washing on Cl element were investigated. The results showed that the municipal sludge's specific resistance to filtration after co-treatment was significantly reduced, and more hydrophobic channels were formed in the vacuum suction filtration of the treated municipal sludge, conducive to efficient water removal. The moisture content of municipal sludge was reduced from 96.0% to 48.3%, and the moisture reduction rate increased from 17.7% to 32.1%. The chemical composition of MSWI FA could effectively promote the dewatering of municipal sludge, among which CaO was the best, followed by CaCl₂ and NaCl, and KCl was the worst. Simultaneously, the municipal sludge showed a good effect on removing Cl from MSWI FA. The minimum Cl content in the mixture after Co-treatment is 1.5%. These results could provide a new way to dispose of MSWI FA and municipal sludge.

Biological Treatment of Fish Processing Saline Wastewater for Reuse as Liquid Fertilizer

The fish processing sector contributes serious organic pollution loads and high salinity to receiving waters. This research aimed to study the effect of salt (NaCl) concentration on the treatment efficiency of fish processing wastewater in a continuous flow system by natural biodegradation. This research also focused on the use of a laboratory-scale bioreactor, which is operated in an aerobic continuous flow system with a 5-day cycle treatment of three different concentrations of diluted fish processing wastewater (30-, 50-, and 100-fold) with salt concentrations varying from 0% to 7% w/v NaCl. The evaluation of system performance at nine different operating hydraulic retention times (HRT) that range from 2–10 days indicated that the substrate removal rates increase with the increase in HRT along with the increasing wastewater concentration. The optimum biomass yield was found at the 8-day HRT, and the highest substrate removal was obtained at 10-day HRT. The study on 11 different salt contents in wastewater at the optimal HRTs of 10, nine, and eight days showed the existence of inhibition effects on biomass growth and substrate removal from 3.0% salt concentration. The treated wastewater without offensive odor is feasible for its reutilization as an environmental friendly liquid fertilizer.

Compression dewatering of municipal activated sludge: effects of salt and pH

Even after mechanical dewatering, activated sludge contains a large amount of water. Due to its composition and biological nature this material is usually highly compressible and known to be difficult to dewater. In the present work, two treatments (salt addition and pH modification) are proposed to highlight some aspects which could explain the poor dewaterability of activated sludge. Dewatering tests are carried out in a pressure-driven device in order to well examine both, filtration and compression stages. Physico-chemical parameters, such as surface charge, hydrophobicity, extracellular polymeric substances (EPS) content and filtrate turbidity are measured on the tested sludge, for a better analysis of dewatering results. The dewatering ability of the sludge is widely linked to the cohesion of the flocculated matrix and the presence of fine particles. Both treatments alter the flocculated matrix and release fine particles. The release of fine particles tends to clog both, the filter cake and the filter medium. Consequently, the filtration rate decreases due to higher resistances to the flow. On another hand, the polymeric matrix breakdown enables to release some water trapped within the floc to the bulk liquid phase and thus facilitates its removal, which tends to decrease the moisture content of the filter-cake. It also impacts the compression dewatering step. The more destroyed structures lead to less elastic cakes and thus a slower primary consolidation stage. At the opposite, the mobility of the broken aggregates within the filter-cake does not seem to be improved by size reduction (the kinetics of the secondary consolidation stage are not significantly modified).