Fate of antibiotic resistance genes (ARGs) in wastewater treatment plant: Preliminary study on identification before and after ultrasonication.

This study collected sludge samples from four different sections of a local wastewater treatment plant in Mikkeli, Finland, for antibiotic resistance genes (ARGs) analysis. Here, we examine the seven representative ARGs in sludge, encoding erythromycin (ermB), tetracycline (tetA, tetC, tetQ, tetW) and sulphonamide (sul1) to check abundance before and after ultrasonication. The class 1 integron (intl1) was also observed as an indicator of antibiotic resistance and horizontal gene transmission. The pre-treatment condition included 10 min of ultrasonication (US) for the sludge sample before freeze-drying. The droplet digital PCR system was used to assess the ARGs from the samples, and it was found that ARGs were not effectively eliminated by pre-treatment. After ultrasonication, tetA, tetC and tetQ did not show any variation but tetW showed 20 copies/ng of lower abundance in digested sludge than raw sludge, and a similar abundance was found in dewatered sludge. For MBR sludge, only ermB showed 1000 copies/ng higher abundance compared to the raw sample and surprisingly it did not show the presence of any other types of ARG. This study provides an overview of the appearance of ARGs in regional municipal sludge for further research reflection.

Dynamics of microbial community and their effects on membrane fouling in an anoxic-oxic gravity-driven membrane bioreactor under varying solid retention time: A pilot-scale study.

Membrane fouling in a membrane bioreactor (MBR) is highly influenced by the characteristics of the influent, the mixed liquor microbial community and the operational parameters, all of which are environment specific. Therefore, we studied the dynamics of microbial community during the treatment of real municipal wastewater in a pilotscale anoxic-oxic (A/O) MBR equipped with a gravity-driven membrane filtration system. The MBR was operated at three different solid retention times (SRTs): 25, 40 and 10 days for a total period of 180 days in Nordic environmental conditions. Analysis of microbial community dynamics revealed a high diversity of microbial species at SRT of 40 days, whereas SRT of 25 days was superior with microbial richness. Production of soluble microbial products (SMP) and extracellular polymeric substances (EPS) was found to be intensely connected with the SRT and food to microorganism (F/M) ratio. Relatively longer operational period with the lowest rate of membrane fouling was observed at SRT of 25 days, which was resulted from the superior microbial community, lowest production of SMP and loosely bound EPS as well as the lower filtration resistance of larger sludge flocs. Abundance of quorum quenching (QQ) bacteria and granular floc forming bacterial genera at SRT of 25 days provided relatively lower membrane fouling tendency and larger floc formation, respectively. On the other hand, substantial amount of various surface colonizing and EPS producing bacteria was found at SRT of 10 days, which promoted more rapid membrane fouling compared with the fouling rate seen at other tested SRTs. To sum up, this research provides a realistic insight into the impact of SRT on microbial community dynamics and resulting characteristics of mixed liquor, floc size distribution and membrane fouling for improved MBR operation.

Electro-dewatering treatment of sludge: Assessment of the influence on relevant indicators for disposal in agriculture.

Waste activated sludge requires effective dewatering, high biological stability and retention of nutrients prior to disposal for agricultural application. The study was conducted to evaluate the impact of pressure-driven electro-dewatering (EDW) on improving sludge characteristics related to disposal in agriculture, including biological stability, pathogen availability, heavy metals concentrations and nutrients content. Thickened conditioned and mechanically dewatered sludge samples were collected from two wastewater treatment plants (WWTPs), characterized by different stabilization processes, and treated by a lab-scale device at 5, 15 and 25 V. EDW increased significantly the dry solid (DS) content, up to 43-45%, starting from 2 to 3% of raw sludge. The endogenous value of specific oxygen uptake rate (SOUR), monitored as indicator of biological stability, increased up to 56% and 39% after EDW tests for sludge from two WWTPs. On the other hand, the exogenous SOUR decreased, indicating a significant drop in the active bacterial population. Likewise, a 1-2 log unit reduction was observed for E. coli after EDW tests at 15 and 25 V. However, no remarkable removal of heavy metals, namely chromium, nickel, lead, copper and zinc, was achieved. Finally, the concentration of nutrients for soil, such as carbon, nitrogen, phosphorus and sulfur, was not affected by the EDW process. In conclusion, EDW exerts considerable effects on the biological characteristics of sludge, which should be considered in a proper design of sludge management to ensure safe and sustainable resource recovery.

HNO2 treatment of sludge: An alternative way of sludge usage as fertilizer.

The research was conducted to evaluate the sludge quality as fertilizer after heavy metal removal by using free nitrous acid (FNA, HNO2) solution. To meet up the Korean criteria of fertilizer, FNA treatment with the ultrasonic process was studied here. The sample was taken from a local wastewater and sewage treatment plants and FNA with FNA plus ultrasonic used to treat them. As and Cd concentrations were met the Korean criteria after FNA treatment. In contrast, Al of sludge from sewage treatment plant did not decrease down to the criteria, possibly suggesting that it may be related to the coagulants of the sludge during thickening and dewatering. FNA treatment showed satisfactory results in comparison with the other acidic treatment of citric acid, oxalic acid, HNO3 or HCl. Removal efficiency of the Fenton-like reaction was more effective than the FNA method. Despite this result, the FNA treatment may be better for sludge recycling as fertilizer because the Fenton-like process removed the necessary organic matter, nitrogen as well as metals. Moreover, the addition of ultrasound process has in conserving time and expenditure in metal removal and FNA with ultrasound became more effective in shorter reaction time. Therefore, FNA treated sludge could be a better option for sludge recycling as fertilizer. In conclusion, a proper plan of sludge management should be required for future work to use sludge as fertilizer.

Optimization of integrated ultrasonic-Fenton system for metal removal and dewatering of anaerobically digested sludge by Box-Behnken design.

This study reveals the optimization of ultrasonic-Fenton process for the treatment of sludge taken from a local municipal wastewater treatment plant after anaerobic digestion. Box-Behnken design (BBD), a common approach of response surface methodology (RSM), was applied to evaluate and optimize the individual and interactive effects of three process variables, namely Fe2+ dose, H2O2 amount and sonication time for Fenton-ultrasonication method. Five dependent parameters including total organic carbon (TOC), extracellular polymeric substances (EPS), as LB-EPS and TB-EPS, and metals such as Zn and Cu were considered as the responses to investigate. According to the results of analysis of variances (ANOVA), five modelling equations are proposed that can be used to operate the design space with high regression coefficient R2. Modelling results suggest that Fenton parameters, such as: H2O2 and Fe2+ dosage had the significant effects on the overall removal of TOC; whereas, sonication improved the metal removal from the sludge sample. Based on response surface methodology, best performance is achievable under the following conditions: 36 mM of Fe2+, 320 mM H2O2 with 30 min of sonication respectively for all of the responses.