Microplastics extraction from wastewater treatment plants: Two-step digestion pre-treatment and application.

As the gathering place of urban wastewater, wastewater treatment plants (WWTPs) are indispensable for removing microplastics (MPs), one of the emerging contaminants of great concern, from cities into the natural environment. A reliable and efficient extraction method for MPs, especially in organic-rich matrices, such as sludge samples, is the basis for studying MPs contamination, while it is still lacking. The digestion process, which requires further optimisation, is the most important step during extraction. In this study, we developed and optimised a two-step digestion process to extract MPs and proposed a recommended dosage of digestion reagents based on the mixed liquid volatile suspended solids (MLVSS) level of the sample. Successive addition of 30% H2O2 + 1 M HNO3 (v:v = 1:1, T = 60 °C, t = 5 h + 5 h) could efficiently extract MPs from sludge samples (over 90%), and the recommended dosage of digestion reagent was 100 ml 30% H2O2+100 ml 1 M HNO3 with the sample MLVSS lower than approximately 0.43 g. This new method was also applied to examine the characteristics of MPs in two typical WWTPs (anaerobic-anoxic-oxic and biofilter processes) in Shenzhen. The concentrations of MPs in the influent, effluent and dewatered sludge were approximately 114.00 n/L, 6.00 n/L, and 126.00 n/g (dry weight) in WWTP A, whereas 404.00 n/L, 22.00 n/L, and 204.00 n/g (dry weight) in WWTP B, respectively. Rayon and polyester were the dominant polymers in both the WWTPs. Fibers accounted for the largest proportion of the influent and effluent. Sizes between 0.20-0.50 mm were most detected. This study provides a new and efficient reference method to extract MPs from WWTPs samples, especially sludge sample, with less MPs loss and more beneficial to subsequent identification.

Isolation and characterization of Shigella flexneri G3, capable of effective cellulosic saccharification under mesophilic conditions.

A novel Shigella strain (Shigella flexneri G3) showing high cellulolytic activity under mesophilic, anaerobic conditions was isolated and characterized. The bacterium is Gram negative, short rod shaped, and nonmotile and displays effective production of glucose, cellobiose, and other oligosaccharides from cellulose (Avicel PH-101) under optimal conditions (40°C and pH 6.5). Approximately 75% of the cellulose was hydrolyzed in modified ATCC 1191 medium containing 0.3% cellulose, and the oligosaccharide production yield and specific production rate reached 375 mg g Avicel(-1) and 6.25 mg g Avicel(-1) h(-1), respectively, after a 60-hour incubation. To our knowledge, this represents the highest oligosaccharide yield and specific rate from cellulose for mesophilic bacterial monocultures reported so far. The results demonstrate that S. flexneri G3 is capable of rapid conversion of cellulose to oligosaccharides, with potential biofuel applications under mesophilic conditions.

Occurrence, effect, and fate of residual microplastics in anaerobic digestion of waste activated sludge: A state-of-the-art review.

The plastic products have large consumption over last decades, resulting in a serious microplastics (MPs) pollution. Specially, the main removal way of MPs from wastewater is to transfer MPs from liquid to solid phase, leading to its enrichment in waste activated sludge (WAS). Anaerobic digestion has been served as the most potential technique to achieve both resource recovery and sludge reduction, herein this review provides current information on occurrence, effect, and fate of MPs in anaerobic digestion of WAS. The effects of MPs on WAS anaerobic digestion are greatly related to forms, particles sizes, contents, compositions and leachates of MPs. Also, the presence of MPs not only can change the effects of other pollutants on anaerobic digestion of WAS, but also can affect the fates of them. Besides, the future perspectives focused on the fate, effect and final removal of MPs during WAS anaerobic digestion process are outlined.

Role of extracellular polymeric substances in enhancement of phosphorus release from waste activated sludge by rhamnolipid addition.

This study investigated the role of extracellular polymeric substances (EPSs) in enhanced performance of phosphorus (P) release from waste activated sludge (WAS) by adding rhamnolipid (RL). Results showed that compared to WAS without pretreatment, the released PO4(3-)-P increased with RL addition from 0 to 0.2 g/gTSS (total suspended solid), and increased by 208% under the optimal condition (0.1 g RL/g TSS and 72-h fermentation time). The cumulative PO4(3-)-P was better fitted with pseudo-first-order kinetic model. Moreover, the contents of metal ions increased in liquid but decreased in EPSs linearly with RL addition increasing, and WAS solubilizations were positively correlated with the released metal ions. The enhanced total dissolved P mainly came from cells and others (69.39%, 2.27-fold higher than that from EPSs), and PO4(3-)-P was the main species in both liquid and loosely bound EPSs, but organic P should be non-negligible in tightly bound EPSs.

Effects of ultrasonic-assisted thermophilic bacteria pretreatment on hydrolysis, acidification, and microbial communities in waste-activated sludge fermentation process.

A novel pretreatment method combining ultrasonic with thermophilic bacteria (Geobacillus sp. G1) was employed to pretreat waste-activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent volatile fatty acids (VFAs) production. The soluble protein and carbohydrate were mostly released from intracellular ultrasonic-assisted Geobacillus sp. G1 pretreatment, and accumulated to 917 ± 70 and 772 ± 89 mg COD/L, respectively, which were 2.53- and 2.62-fold higher than that obtained in control test. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, indicating the synergistic effect of ultrasonic and Geobacillus sp. G1 pretreatments on WAS hydrolysis. The maximum VFAs accumulation was 4437 ± 15 mg COD/L obtained in ultrasonic-assisted Geobacillus sp. G1 pretreatment test. High-throughput pyrosequencing analysis investigated that the microbial communities were substantial determined by the pretreatment used. The hydrolysis enhancement was caused by an increase in extracellular enzymes, which was produced by one of dominant species Caloramator sp. The positive effect was well explained to the enhancement of WAS hydrolysis and final VFAs accumulation.