Mechanisms of ZnO Nanoparticles Enhancing Phototransformation of Biologically Derived Organic Phosphorus in Aquatic Environments.

Zinc oxide nanoparticles (ZnO NPs), as the highly efficient photocatalysts, could enhance the transformation of biogenic organic phosphorus (OP) to orthophosphate (PO43-) by photodegradation, accelerating eutrophication. Conversely, orthophosphate can also transform ZnO NPs and thus potentially alter their catalytic and chemical properties. Here, we investigated the transformation mechanisms of three biogenic OP compounds and ZnO NPs under ultraviolet light (UV) illumination: inositol phosphates (IHPs), nucleic acids (DNA), and aminoethylphosphonic acid (AEP). The physicochemical characteristics of the resulting products were systematically characterized. Results show that ZnO NPs accelerated the transformation of IHPs, DNA, and AEP to inorganic phosphorus with the direct photolysis efficiencies of 98.14, 87.68, and 51.76%, respectively. The main component of the precipitates remained ZnO NPs, and Zn3(PO4)2 was identified. Zinc phytate was determined in the ZnO NP-IHP system. 31P NMR and FTIR further confirmed that the aquatic phase contained orthophosphate. Photoproduced hydroxyl (·OH) and superoxide (·O2-) were proved to play a dominant role in the OP photomineralization. Furthermore, ZnO NPs significantly enhanced the intensity of ·OH and ·O2- compared to the OP and Zn2+ solution alone. This work explored the light-induced mineralization processes of OP with ZnO NPs indicating that nanophotocatalysts may play a positive role in transformation of OP species in aquatic environments to further contribute to eutrophication.

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review.

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

Nutrient dynamics and microbial community response in macrophyte-dominated lakes: Implications for improved restoration strategies.

Although lakes dominated by macrophytes are conducive to ecological balance, this balance is easily disrupted by excessive nutrients flowing into the lake. However, knowledge of whether excessive nutrients lead to different microbial environmental vulnerabilities in the lake sediment between macrophyte-dominated areas and macrophyte-free areas is a prerequisite for the implementation of targeted protection measures. In this study, we investigated bacterial communities in sediments using high-throughput sequencing of 16S rRNA genes. Our results showed that the sources of total nitrogen (TN) and organic matter (OM) were related to the macrophytes. The structure, drivers, and interspecific associations of bacterial community, which were more susceptible to increased changes in TN and OM, differed significantly between macrophyte-dominated areas and macrophyte-free areas. More precisely, the lake edge, where was occupied by macrophytes, had a higher proportion of deterministic phylogenetic turnover (88.89%) than other sites, as well as a wider ecological niche and a tighter network structure. Further, as the difference in TN increased, the main assembly processes in surface sediments changed from stochastic to deterministic. However, the majority of phyla from the lake edge showed a greater correlation with excessive nutrients, and the selection of the community by excessive nutrients was more obvious at the edge of the lake. In addition, our results demonstrated that the stability of the bacterial community in macrophyte-free areas is greater than in macrophyte-dominated areas, while an excessively high deterministic process ratio and nutrient (TN and OM) concentration significantly reduced bacterial community stability at macrophyte-dominated areas. Taken together, these results provide a better understanding of the effects of excessive nutrients derived from macrophytes on bacterial community patterns, and highlight the importance of avoiding the accumulation of TN and OM in macrophyte-dominated areas to enhance the sustainability of the ecosystem after restoration of lakes with macrophytes.

Phosphorus complexation of sewage sludge during thermal hydrolysis with different reaction temperature and reaction time by P K-edge XANES and 31P NMR.

Thermal hydrolysis pretreatment (THP) can improve sludge disintegration and biogas production. Phosphorus (P) is immobilized on hydrochars of sewage sludge (SS). It is critical to understand changes in P speciation in SS hydrochars under different reaction temperatures and reaction times during THP for reclamation and (re)cycling of P. This study combined sequential extraction, 31P liquid and solid-state nuclear magnetic resonance (NMR), and P K-edge X-ray absorption near edge structure (XANES) spectroscopy to systematically analyze variation in P speciation and related metals in hydrochars. The temperature of the THP has more influence on P extraction content than reaction time; the bioavailability of P from hydrochars declined with increasing temperature. A 31P liquid and solid-state NMR analysis demonstrated that orthophosphate was the most abundant phosphate present small deviations in the chemical shift were observed in different samples under different conditions. The results of XANES demonstrated that CaP was more stable than FeP and AlP. LCF results suggested OcataCa proportion raised under stable CaP ratio in samples when the temperature was above 155 °C and duration was 60 min. This study provides a theoretical basis that can meet the practical application of THP for sludge disposal and P reclamation on subsequent anaerobic digestion.