Sulfite pretreatment enhances the medium-chain fatty acids production from waste activated sludge anaerobic fermentation

Enhancing medium-chain-length polyhydroxyalkanoate (mcl-PHA) synthesis in mixed microbial cultures via targeted substrate composition: A meta-omics guided approach

This study investigates how varying medium-chain fatty acid (MCFA) ratios in substrates (caproate-rich [C6], heptanoate-rich [C7], octanoate-rich [C8], and Control) affect medium-chain-length PHA (mcl-PHA) synthesis in mixed microbial cultures, assessing their impacts on PHAs yield and PHA monomer composition. Results demonstrate that increasing MCFA concentrations enhanced total PHAs accumulation. Maximum PHAs production was achieved with a caproate-rich substrate (5:1 ratio), yielding 63 wt% of PHA (26% mcl-PHA), while heptanoate-rich substrate (5:1 ratio) produced 58 wt% of PHA (29% mcl-PHA). In contrast, octanoate-rich substrates resulted in significantly lower mcl-PHA fractions (20%), attributed to β-oxidation-driven precursor depletion. Metagenomic analysis revealed substrate-dependent microbial community shifts, alongside differential expression of β-oxidation genes (FadD, FadE, FadA) and PHA synthases genes (PhaC). These findings highlight the critical role of MCFA composition in optimizing mcl-PHA biosynthesis, demonstrating that tailoring MCFA ratios in feedstocks enhances production efficiency and enables scalable and sustainable biopolymer synthesis from renewable waste resources.

Calcium peroxide treatment of cyanobacterial blooms: Ecological safety assessment on submerged macrophyte Vallisneria natans

The outbreak of cyanobacterial blooms poses an increasingly serious ecological challenge. Our previous study found that calcium peroxide (CaO2) has a high inhibitory effect on cyanobacteria, along with a practical application potential in cyanobacteria-dominated lakes. In order to explore the sensitivity of aquatic ecosystems to CaO2 treatment, we conducted this study to elucidate the ecological impact of CaO2 on Vallisneria natans (V. natans) when inhibiting cyanobacterial bloom. This study firstly optimized the performance of CaO2 by preparing alginate-encapsulated CaO₂ (CaO2-Bead), which prolonged the release time of reactive oxygen species (ROS). Subsequently, the sensitivity of submerged plant V. natans and its biofilm was explored. After adding 100 mg L-1 CaO2-Bead, significant inhibitory effect on cyanobacteria was found, and the inhibition rate of cyanobacterial biomass reached 93.5 %. More importantly, CaO2-Bead can alleviate the oxidative stress, effects of Extracellular Polymeric Substances (EPS) structure and microbial community on the surface of leaf biofilm caused by cyanobacteria. At the same time, it decreased the damage of photosynthesis, mitochondrial transport, plant-pathogen interaction, mitogen-activated protein kinases (MAPK), and ubiquitin-mediated protein degradation in pathways in V. natans under inhibition of cyanobacteria. Our research provides a theoretical basis for evaluating the safety of CaO2 on the aquatic environment when treating cyanobacterial blooms.

Aerobic granular sludge enhances start-up and granulation in single-stage partial nitritation anammox granular sludge systems: Performance, mechanism, and shifts in bacterial communities

The rapid start-up and granulation of a single-stage partial nitritation anammox granular sludge (PN/AnGS) system under limited seed sludge conditions is crucial for its practical application. This study proposed an aerobic granular sludge (AGS) - based strategy, enhanced the enrichment of anammox bacteria (AnAOB), and shortened the start-up time of PN/AnGS system by 20.5%. In addition, the inoculation of AGS can ensure the stable operation of the system during the selective sludge discharge to washout the flocs. Microbial community structure, particle size distribution, morphology results showed that niche shift was the key to promote the enrichment of AnAOB, and AGS played a decisive role in the particle characteristics of PN/AnGS. Since AGS can be directly obtained from full-scale AGS wastewater treatment plants, integrating PN/AnGS with AGS processes can transition wastewater treatment from a "linear economy" to a "circular economy", enhancing nitrogen removal efficiency and delivering significant economic and environmental benefits.

Insight into the responses of the anammox granular sludge system to tetramethylammonium hydroxide (TMAH) during chip wastewater treatment

Tetramethylammonium hydroxide (TMAH), an extensively utilized photoresist developer, is frequently present in ammonium-rich wastewater from semiconductor manufacturing, and its substantial ecotoxicity should not be underestimated. This study systematically investigated the effects of TMAH on the anammox granular sludge (AnGS) system and elucidated its inhibitory mechanisms. The results demonstrated that the median inhibitory concentration of TMAH for anammox was 84.85 mg/L. The nitrogen removal performance of the system was significantly decreased after long-term exposure to TMAH (0-200 mg/L) for 30 days (p < 0.05), but it showed adaptability to certain concentrations (≤50 mg/L). Concurrently, the stability of the granules decreased dramatically, resulting in the breakdown of AnGS. Further investigations indicated that TMAH exposure increased the secretion of extracellular polymeric substances but weakened their defense function. The increase in reactive oxygen species resulted in damage to the cell membrane. Reduced activity of anammox bacteria, impeded electron transfer, and changes in enzyme activity suggested that TMAH affected the metabolic activity. Microbiological analysis revealed that TMAH caused a decrease in the abundance of anammox bacteria and a weakening of symbiotic interactions within the microbial community. These results provide valuable guidance for the AnGS system application in chip wastewater treatment.

The enhancement of caproic acid synthesis from organic solid wastes: A review

Organic solid waste (OSW) significantly harms the environment and threatens human health. Producing caproic acid (CA) from OSW presents a cost-effective, sustainable, and resource-efficient solution. This study comprehensively examines the various methods for synthesizing CA from OSW, focusing on waste material selection, pretreatment processes to improve dissolution and hydrolysis of OSW, key substrates, and optimization strategies. Using OSW resources has been extensively studied and applied across numerous industries, presenting a promising solution for reducing environmental pollution. This study provides insights into CA synthesis pathways and substrate selection while emphasizing the optimization of CA production from OSW. It also highlights key areas for future research.

Influence of acetate-to-butyrate ratio on carbon chain elongation in anaerobic fermentation

This study investigated the effect of electron acceptor (EA) distribution (acetate to butyrate ratio) on the carbon chain elongation (CCE) process. The results showed that the higher content of butyrate in the initial material led to the higher production of caproate. The maximum production of caproate was 3.74 ± 0.30 g·L-1, which was obtained when only butyrate was added as EA. Little caproate but much butyrate was produced where only acetate was added as EA. This indicated that CCE bacteria preferentially selected acetate as the EA to produce butyrate, and butyrate could be selected as EA to produce caproate only when the acetate content was much lower than butyrate. Unclassified_f_Dysgonomonadaceae, Massilibacterium, and Seramator were the predominant bacteria. Functional enzyme analysis showed that high butyrate content strengthened the fatty acid biosynthesis pathway and reverse β-oxidization pathway. The findings showed the importance of butyrate in CCE for caproate production.