Sewage sludge reduction and system optimization in a catalytic ozonation process

Prediction of varying microcystins during non-thermal plasma oxidation of harvested microalgal biomass

By capturing intracellular microcystins (MCs) release from microalgal cell destruction and extracellular MCs oxidation, this study suggests a mathematical model explaining the simultaneous removal of microalgae and their toxins (MC-LR, -RR, and -YR) in non-thermal plasma (NTP) application. Although the suggested model was built based on simplified kinetic assumptions, it can reasonably predict the behavior of extracellular MCs in a harvested/concentrated slurry of microalgae taken from a blooming site. After 24 h of NTP treatment, the experimental reduction of extracellular MCs was recorded up to ∼77 %. Regressions based on the experimental data reveal the degradation rate (8.60 d^-1) and release rate (0.37 d^-1) of MCs, which provides the essential physicochemical information about intracellular MCs release by microalgal cell destruction. Simulation results help to develop safe and useful control over the simultaneous treatment of harvested microalgal biomass and toxins. This study further demonstrates that the suggested model contributes to predicting the variation of MCs in mass management of microalgal biomass for sustainable utilization.

Reduction of the excess sludge production by biological alternating process: real application results and metabolic uncoupling mechanism

The biological solution proposed to reduce the wasted sludge production is based on a process of alternating phases realized in a specific reactor (alternate cycles in sludge line (ACSL)) where a quote of the recycle sludge is treated and sent back to the main activated sludge process. The ACSL process was applied in two urban wastewater treatment plants (WWTPs). The reduction was tested by changing the hydraulic retention time and the conditions of oxidation reduction potential. The main mechanism of the process is recognized in the metabolic uncoupling. In fact, an increase in the specific oxygen uptake rate in the biological reactors was recorded (up to 20 mg/g VSS/h), which was stimulated by the fasting condition in the ACSL. The process is able to reduce the observed sludge yield on average of 25-30% with final average values reaching 0.179 kg VSS/kg chemical oxygen demand (COD) for WWTP1 and 0.117 kg VSS/kg COD for WWTP2.

Study on a novel reactor of sludge process reduction for domestic sewage treatment

A laboratory-scale novel Sludge Reduction Reactor with Arc Guide Plate (SRR) for sludge process reduction was developed in this study. Pollutant removal efficiency and biomass yield for domestic sewage treatment in the Anaerobic/Anoxic/Oxic-SRR (A2/O-SRR) process were compared with performances in a control A2/O process. One of the competitive advantages in the SRR was that part of the inert suspended solids (ISS) could be separated and discharged out of system with flux at the bottom of the SRR. Mixed liquid volatile suspended solids (MLVSS) in the A2/O-SRR system also could be steadily kept at a good level under a relatively long solid retention time. The average MLVSS/mixed liquor suspended solids (MLSS) ratio of 77.5% in the A2/O-SRR was higher than that in the A2/O process. Average removal rates of chemical oxygen demand (COD), total nitrogen (TN) and NH4(+) showed little difference, while total phosphorous (TP) removal efficiency in the A2/O-SRR decreased slightly (81.89% in the A2/O-SRR and 86.50% in the A2/O process) due to the reduction of sludge discharge. The A2/O-SRR system demonstrated a considerable sludge reduction effect, with the sludge reduction ratio of 43.8%, lower solid volume index and higher dehydrogenase activity (DHA) value in comparison to the control A2/O system. The mainly mechanisms of sludge reduction in the SRR have been proved to be the uncoupling effect under the condition of anaerobic/oxic circulation and the sludge lysis with the lack of substrate.