Research on the Resource Recovery of Medium-Chain Fatty Acids from Municipal Sludge: Current State and Future Prospects.

The production of municipal sludge is steadily increasing in line with the production of sewage. A wealth of organic contaminants, including nutrients and energy, are present in municipal sludge. Anaerobic fermentation can be used to extract useful resources from sludge, producing hydrogen, methane, short-chain fatty acids, and, via further chain elongation, medium-chain fatty acids. By comparing the economic and use values of these retrieved resources, it is concluded that a high-value resource transformation of municipal sludge can be achieved via the production of medium-chain fatty acids using anaerobic fermentation, which is a hotspot for future research. In this study, the selection of the pretreatment method, the method of producing medium-chain fatty acids, the influence of the electron donor, and the technique used to enhance product synthesis in the anaerobic fermentation process are introduced in detail. The study outlines potential future research directions for medium-chain fatty acid production using municipal sludge. These acids could serve as a starting point for investigating other uses for municipal sludge.

Further study on particle size, stability, and complexation of silver nanoparticles under the composite effect of bovine serum protein and humic acid.

Silver nanoparticles (AgNPs) are widely used due to their unique antibacterial properties and excellent photoelectric properties. Wastewater treatment plants form a pool of AgNPs due to the social cycle of wastewater. During biological treatment processes, the particle size and stability of AgNPs change. We studied the particle size changes and stability of silver nanoparticles in the presence of bovine serum albumin (BSA) and humic acid (HA). The experimental results indicated that silver nanoparticles can complex with the functional groups in BSA. For AgNP-BSA composites, as the BSA concentration increases, the size of the silver nanoparticles first decreases and then increases. AgNPs can combine with the amide, amino, and carboxyl groups in HA. As the concentration of HA increases, the particle size and large particle size distribution of AgNPs increase. This increasing trend is more obvious when the HA concentration is lower than 20 mg L-1. When HA and BSA exist at the same time, HA will occupy the adsorption sites of BSA on the surface of AgNPs, and the AgNP-HA complex will dominate the system. This study aims to provide key operational control strategies for the process operation of wastewater treatment plants containing AgNPs and theoretical support for promoting water environment improvement and economic development such as tourism.

Granule formation mechanism, key influencing factors, and resource recycling in aerobic granular sludge (AGS) wastewater treatment: A review.

The high-efficiency and additionally economic benefits generated from aerobic granular sludge (AGS) wastewater treatment have led to its increasing popularity among academics and industrial players. The AGS process can recycle high value-added biomaterials including extracellular polymeric substances (EPS), sodium alginate-like external polymer (ALE), polyhydroxyfatty acid (PHA), and phosphorus (P), etc., which can serve various fields including agriculture, construction, and chemical while removing pollutants from wastewaters. The effects of various key operation parameters on formation and structural stability of AGS are comprehensively summarized. The degradable metabolism of typical pollutants and corresponding microbial diversity and succession in the AGS wastewater treatment system are also discussed, especially with a focus on emerging contaminants removal. In addition, recent attempts for potentially effective production of high value-added biomaterials from AGS are proposed, particularly concerning improving the yield, quality, and application of these biomaterials. This review aims to provide a reference for in-depth research on the AGS process, suggesting a new alternative for wastewater treatment recycling.

Material biosynthesis, mechanism regulation and resource recycling of biomass and high-value substances from wastewater treatment by photosynthetic bacteria: A review.

The environmental-friendly and economic benefits generated from photosynthetic bacteria (PSB) wastewater treatment have attracted significant attention. This process of resource recovery can produce PSB biomass and high-value substances including single cell protein, Coenzyme Q10, polyhydroxyalkanoates (PHA), 5-aminolevulinic acid, carotenoids, bacteriocin, and polyhydroxy chain alkyl esters, etc. for application in various fields, such as agriculture, medical treatment, chemical, animal husbandry and food industry while treating wastewaters. The main contents of this review are summarized as follows: physiological characteristics, mechanism and application of PSB and potential of single cell protein (SCP) production are described; PSB wastewater treatment technology, including procedures and characteristics, typical cases, influencing factors and bioresource recovery by membrane bioreactor are detailed systematically. The future development of PSB-based resource recovery and wastewater treatment are also provided, particularly concerning PSB-membrane reactor (MBR) process, regulation of biosynthesis mechanism of high-value substances and downstream separation and purification technology. This will provide a promising and new alternative for wastewater treatment recycling.

Chemical fractionation and risk assessment of surface sediments in Luhun Reservoir, Luoyang city, China.

To understand the potential risks of heavy metals, including their bioavailability and toxicity, 15 surface sediment samples were collected from Luhun Reservoir in Luoyang city, China. Total concentrations and chemical fractions of Cd, Cr, Cu, Ni, Pb, and Zn were analyzed. Various rating methods were used to evaluate the degree, risk, and toxicity of the heavy metal pollution. Results showed that Cd and Pb were preferentially associated with exchangeable (55.77-69.76%) and reducible (53.54-69.43%) fractions, respectively, and therefore exhibited high potential availability. Cr (57.14-86.56%) and Ni (32.21-72.77%) occurred primarily in the residual fraction. Metal concentrations in the effective fraction of the sediment decreased in the order: Cd (96.32%) > Pb (91.61%) > Cu (64.54%) > Zn (57.23%) > Ni (41.51%) > Cr (21.68%). Risk assessment indicated that the risk for Cd is extremely high (62.96%); Cu, Pb, and Zn are ranked as medium risk. Based on the potential ecological risk index, these metals (especially Cd) showed higher potential risk near the dam region. Toxic unit values (2.89-6.05) in more than 60% of sediment sites exceeded a value of 4, and Pb had a relatively higher contribution (1.06-2.65). Cd and Pb are the main contaminants in sediments of Luhun Reservoir and should be paid more attention in the future.