A mesophilic (35°C) continuous co-digestion experiment of sewage sludge and softened pre-treated rice straw (RS) was conducted in the present study to evaluate the impact on the dissolved organic matters (DOMs) in the digested sludge due to the addition of RS. Sludge retention time was 25 d; total solids (TS) of sewage sludge and RS were 3% and 1.5%, respectively. Methane yields of sludge digestion, RS digestion and co-digestion were 0.27, 0.11 and 0.25 L/g-COD_Cr, respectively. The degradation of RS caused significant increase in dissolved organic carbon (DOC) in digested sludge, and humic matter concentration increasing by over 10 folds. Results of excitation-emission matrix (EEM) fluorescence spectroscopy revealed that the addition of RS caused additional fluorescent peak that related to humic acid-like substances in the digested sludge. The digested supernatant was then mixed with activated sludge [mixing ratio: 10: 1 (vol./vol.)] and cultured under aerobic condition to study the biodegradability of DOMs. Results of DOMs analysis and EEM spectra of filtrate samples after aerobic treatment showed that organic content in digested sludge was resistant to biodegrade.

Bacteria play a major role in removal of pollutants in activated sludge processes, but the reason why bacterial population changes is not yet clearly understood. This study focused on the chemicals produced by microorganisms in activated sludge. Chemical components in an activated sludge from a laboratory sequencing batch reactor (Lab SBR) was extracted with ethanol, and activated sludges from two sources, Lab SBR and a wastewater treatment plant (WWTP) were incubated with and without the extracted chemicals. Incubation was performed on a microplate which has 96 wells and each of the well is regarded as a small activated sludge reactor. After 24 hours incubation, activated sludge samples were recovered, and their microbial populations were analyzed by reverse transcription PCR (RT-PCR) targeting a partial 16S rRNA gene sequence followed by pyrosequencing. The results were preliminary, but clearly showed that bacterial population changed significantly when activated sludge was incubated with ethanol-extract addition. In addition, activated sludge from Lab SBR and WWTP were similarly affected by the extract.

Microcystin-LR (MC-LR) is one of the most frequent and most lethal toxicants and a vital environmental pollutant due to its toxicity and persistence. It is hepatotoxins and have been shown to be potent tumor-promoters which pose a serious threat to human health in the form of chronic exposure through drinking water. In this study, a novel electrochemical method for the determination of MC-LR has been developed using protein phosphatase 2A (PP2A) enzyme inhibition. The rapid and simple determination of PP2A activity was accomplished by means of hydrodynamic voltammetry in a 50 µL micro-droplet with a rotating disk electrode (RDE). The chronoamperometric response were obtained from the electrochemical oxidation of p-aminophenol (PAP) following the enzymatic conversion of p-aminophenyl phosphate (PAPP) as a substrate. PP2A activity estimated by using PAPP substrate is affected by MC-LR, and this phenomenon decreases the current signal of PAP. The IC₅₀ value was calculated as 0.08 µg/L which is well below the World Health Organization (WHO) provisional guideline value for total MC-LR of 1 µg/L in drinking water. The enzymatic reaction using RDE is possible to perform using fewer chemicals in a rapid manner. Therefore, the method can be very attractive for MC contaminated drinking water routine assessment.

In 2016, only 56.7% of the lakes and reservoirs in Japan complied with the standard of chemical oxygen demand determined by permanganate (COD_Mn). The dissolved organic matter (DOM) contributing to COD_Mn in lakes is heterogenous in nature; hence, DOM compositions in different lake waters are not well known. In this study, molecular components contributing to dissolved COD_Mn (DCOD_Mn) in lake water were identified via high-resolution Orbitrap mass spectrometry (Orbitrap MS). Water samples were collected from Lake Inba in September 2016. The filtered samples were oxidized by KMnO₄ according to the JIS method K0102 for different durations (ranging between 0–120 min). The DOM extracted via solid phase extraction was analyzed using Orbitrap MS, and molecular formulas were assigned. In all, 1,115 components were observed before oxidation. During time-course oxidation, components with higher unsaturation were selectively oxidized, suggesting that they contributed to the DCOD_Mn in lake water. DCOD_Mn components were screened for DOM in Lake Inba, and other DOM references were isolated from the Suwannee River and Lake Biwa. Only 14%–32% of the total components were regarded as DCOD_Mn components, indicating the limited coverage of COD_Mn. The compositions of DCOD_Mn components were highly diverse, depending on the sources.

The study was aimed at developing an alternative method to catch biodegradable concentrations in municipal wastewater, especially for designing wastewater treatment plants receiving storm water where the influent concentrations significantly changed in time. As conventional water analytical methods required lots of samples and numerous analysis, which was practically infeasible, a lab-scale nitrifying activated sludge reactor having on-line DO meter and quick-test nitrate kit was installed at the experimental site in Hue, Vietnam. By fixing the hydraulic retention time with 2.0 hours and aeration intensity, the biodegradable concentrations in the influent including carbonaceous and nitrogenous compounds were back-calculated from the dynamic response of dissolved oxygen concentration in the aeration tank and the nitrate concentration in the effluent using IWA Activated Sludge model. During the data collection event for 24 hours, the influent was also sampled at 1-hr interval and its concentrations were compared with those calculated. The field experiment successfully demonstrated that the back-calculation method could reasonably estimate the influent biological concentration on the basis of biological oxygen demand where the concentration was highly fluctuated in time. Based on the experiment, the feasibility to measure sudden elevation and decrease of pollutant load in the first flush was discussed in the paper.

The effects of sulfates on enhanced biological phosphorus removal (EBPR) were investigated in three municipal wastewater treatment plants (WWTPs), which treat sewage containing several concentrations of sulfates. The behaviour of sulfates and phosphates in the anaerobic oxic process was analysed by considering the daily inflow rate and water quality. Although phosphorus release and uptake were recognized in all plants, phosphorus release from the WWTPs that were treating high-sulfate wastewater (high-sulfate WWTP), was lower than that of the WWTP treating low-sulfate wastewater (low-sulfate WWTP). In the high-sulfate WWTPs, sulfate decreased in the anaerobic zone and increased in the oxic zone. Analysis of the sulfate reduction and sulfur oxidation activities of the sludge showed that both activities were dependent on the influent sulfate concentration. The relative abundance of SRB which oxidize organic matters completely in high-sulfate WWTPs tends to be higher than that in low-sulfate WWTPs. On the other hand, a lower relative abundance of polyphosphate accumulating organisms (PAOs) was recognized in the high-sulfate WWTPs.