Deep insights into the roles and microbial ecological mechanisms behind waste activated sludge digestion triggered by persulfate oxidation activated through multiple modes

Study on short-chain fatty acids production from anaerobic fermentation of waste activated sludge pretreated by alkali-activated ammonium persulfate

As a sustainable method for carbon recovery from waste activated sludge (WAS), anaerobic fermentation to produce short-chain fatty acids (SCFAs) is often limited by disintegration of WAS. A novel pretreatment method of alkaline-activated ammonium persulfate (AP/Alk), employing an initial pH of 10 and an ammonium persulfate dosage of 1 mM/g VSS (mmol per gram volatile suspended solids), was proposed in this study to enhance disintegration of WAS and yield of SCFAs. It was compared with one control and five pretreatment groups including alkali, persulfate, free ammonia, ammonium persulfate, alkali-activated sodium persulfate to elucidate the synergistic effects of free ammonia and radicals in WAS dissolution and acidogenesis within the AP/Alk system. The highest sludge disintegration degree with 30.3 % and maximum SCFAs production with 295.4 mg COD/g VSS were achieved by using the method. Comparative analysis showed that free ammonia primarily disrupted microbial cells to release intracellular organics, while radicals preferentially degraded tightly bound extracellular polymeric substances (TB-EPS) proteins. The synergistic effects of free ammonia and radicals accelerated accumulation of soluble proteins and polysaccharides, improved selectively enrichment of hydrolytic-acidogenic genera (e.g., Macellibacteroides, Proteiniclasticum, Desulfobulbus), and upregulated antioxidant genes to alleviate oxidative stress, but suppressed SCFAs consumers (e.g., unclassified_f__Comamonadaceae) including methanogens (e.g., Methanosaeta), thereby promoting the accumulation of SCFAs and acetic acid proportion. AP/Alk offers a sustainable strategy for WAS utilization and energy recovery.

Mechanistic elucidation of ultraviolet light and peracetic acid coupling-driven enhancements in short-chain fatty acid production from sludge: Reactive species-induced organic solubilization and microbial function regulation

This study investigates the potential of enhancing short-chain fatty acid (SCFA) production during anaerobic fermentation of waste activated sludge through ultraviolet (UV) and peracetic acid (PAA) treatment. Under optimal conditions (UV irradiation time = 60 min and PAA dosage = 0.03 g/g VSS (volatile suspended solids), UV/PAA pretreatment enhanced sludge solubility, improved the biodegradability of organic matter, and facilitated pollutant degradation. During anaerobic fermentation, UV/PAA treatment resulted in an 836 % increase in SCFA production and a 50 % higher acetic acid ratio compared to the control group. Mechanistic studies revealed that UV/PAA treatment promoted sludge decomposition and enhanced the biodegradability of dissolved organic matter by generating more reactive species (•OH, CH3C(O)O•, •O2-, and 1O2), thereby facilitating sludge hydrolysis and acidification. Additionally, UV/PAA treatment increased the abundance of hydrolytic and SCFA-producing bacteria while reducing the abundance of SCFA-consuming bacteria. Moreover, UV/PAA treatment stimulated the expression of key enzyme genes involved in organic matter hydrolysis and SCFA production, thereby promoting SCFA accumulation. Therefore, UV/PAA treatment is promising in sludge treatment and provides a new approach for resource recovery from sludge.

Improved volatile fatty acid production in anaerobic digestion via simultaneous temperature regulation and persulfate activation by biochar: Chemical and biological response mechanisms

Increasing volatile fatty acid (VFA) production via persulfate activation (i.e., chemical effect) in anaerobic digestion (AD) is an emerging resource utilization method. However, the reaction mechanisms responsible for improving VFA production in AD via simultaneous temperature regulation and persulfate activation by biochar remain unclear. In this study, three PB15 treatment systems of low temperature (15 °C), medium temperature (35 °C) and high temperature (55 °C) were set to explore the relationship between VFAs production and treatment temperature and the influence of temperature on the reaction mechanism. The results show that the improvement of hydrolysis and acidification efficiency of the system in the medium temperature system is the highest. The VFA yield and acid production rate in the treatment group at 35 °C were 2.49 and 5.22 times higher than those in the control group, respectively. The chemical effect effectively initiated the anaerobic acid production process and maintained the dominant role of the biological effect. The activity of persulfate is too low at low temperature, and its decomposition is too fast at high temperature. Plenty of free radicals lead to enhanced oxidation of the system, which may kill the fermentation bacteria. The NCM model indicates that microbial stability is reduced in high temperature systems. The SEM model showed that temperature change mainly affected substrate degradation by hydrolytic bacteria and indirectly affected acid production by acid-producing bacteria. This study provides a new strategy for realizing pollutant recycling and increasing VFAs production in cold area.