Search

Wastewater sludge is used as an alternative fuel due to its high organic content and calorific value. However, influent characteristics and operational practices of wastewater treatment plants (WWTPs) can increase the sulfur content of sludge, devaluing it as a fuel. Thus, we investigated the biochemical mechanisms that elevate the sulfur content of sludge in a full-scale industrial WWTP receiving wastewater of the textile dyeing industry and a domestic WWTP by monitoring the sulfate, sulfur, and iron contents and the biochemical transformation of sulfate to sulfur in the wastewater and sludge treatment streams. A batch sulfate reduction rate test and microbial 16S rRNA and dsrB gene sequencing analyses were applied to assess the potential and activity of sulfate-reducing bacteria and their effect on sulfur deposition. This study indicated that the primary clarifier and anaerobic digester prominently reduced sulfate concentration through biochemical sulfate reduction and iron–sulfur complexation under anaerobic conditions, from 1247 mg/L in the influent to 6.2~59.8 mg/L in the industrial WWTP and from 46.7 mg/L to 0~0.8 mg/L in the domestic WWTPs. The anaerobic sludge, adapted in the high sulfate concentration of the industrial WWTP, exhibited a two times higher specific sulfate reduction rate (0.13 mg SO42−/gVSS/h) and sulfur content (3.14% DS) than the domestic WWTP sludge. Gene sequencing analysis of the population structure of common microbes and sulfate-reducing bacteria indicated the diversity of microorganisms involved in biochemical sulfate reduction in the sulfur cycle, supporting the data revealed by chemical analysis and batch tests. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) are a promising technology that directly converts organic matter (OM) in wastewater into electricity while simultaneously degrading contaminants. However, MFCs are insufficient for the removal of nitrogenous compounds. Therefore, the post-treatment of MFCs is essential. This study was the first to use natural zeolite adsorption integrated with photosynthesis (ZP) for post-treating MFCs. In this system, no external energy was required; instead, natural light was used to promote the growth of photosynthetic microorganisms, thereby enhancing contaminants removal through the photosynthesis process. To assess the effectiveness of the method, comparisons were conducted under two conditions: dark (no photosynthesis) and light (with photosynthesis). In darkness, extending hydraulic retention time (HRT) enhanced COD and BOD removal by 19.8% and 28.9%, respectively. When exposed to natural light, improvements were even more notable, with COD and BOD removal reaching 32% and 40%, respectively. In both conditions, the method effectively removed NH 4 + , achieving 60% efficiency in darkness and 84.5% in light. This study showed that the adsorption capacity of the zeolite reached saturation when the cumulative liquid volume per unit weight of the zeolite exceeded 0.2 L g -1 . The key functional photosynthetic microbes were investigated using 16S rRNA and 18S rRNA. This revealed the presence of microorganisms such as Chlorobium , Acidovorax , Novosphingobium , and Scenedesmus , which likely play a role in enhancing the efficiency of photosynthesis in removing contaminants. The study findings indicated that the integration of MFCs-ZP represents an eco-friendly approach capable of resource recovery from wastewater while also meeting discharge standards., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Microbial fuel cells (MFCs) show promise in sewage treatment because they can directly convert organic matter (OM) into electricity. This study aimed to demonstrate MFCs stability over 750 days of operation and efficient removal of OM and nitrogenous compounds from sewage. To enhance contaminant removal, oxygen was provided into the anode chamber via a mini air pump. This pump was powered by the MFCs' output voltage, which was boosted using a DC-DC converter. The experimental system consisted of 12 sets of cylindrical MFCs within a 246L-scale reactor. The boosted voltage reached 4.7 V. This voltage was first collected in capacitors every 5 min and then dispensed intermittently to the air pump for the MFCs reactor in 4 s. This corresponds to receiving average DO concentration reaching 0.34 ± 0.44 mg/L at 10 cm above the air-stone. Consequently, the degradation rate constants (k) for chemical oxygen demand (COD) and biological oxygen demand (BOD) in the presence of oxygen were 0.048 and 0.069, respectively, which surpassed those without oxygen by 0.039 and 0.044, respectively. Aeration also marginally improved the removal of ammonia because of its potential to create a favorable environment for the growth of anammox and ammonia-oxidizing bacteria such as Candidatus brocadia and Nitrospira. The findings of this study offer in-depth insight into the benefits of boosted voltage in MFCs, highlighting its potential to enhance contaminant degradation. This serves as a foundation for future research focused on improving MFCs performance, particularly for the removal of contaminants from wastewater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)