Bubbleless Air Shapes Biofilms and Facilitates Natural Organic Matter Transformation in Biological Activated Carbon

Pre-treatment of excess sludge with sulfide-containing wastewater for composite electron donor formation to enhance denitrification

Utilizing the fermentation liquor of excess sludge (ES) for the denitrification process represents an effective strategy for the valorization of ES and achieving environmentally friendly denitrification. However, ES fermentation technologies require significant energy or chemical product inputs. The present study proposes a novel method utilizing sulfide-containing wastewater to pretreat ES for generating dissolved organic matter (DOM), with sulfides and DOM collectively forming a composite electron donor (S-ES-DOM). The introduction of S-ES-DOM enables the establishment of integrated autotrophic and heterotrophic denitrification (IAHD) process, achieving 100 % denitrification efficiency. Molecular analysis identified an increase in biodegradable components within S-ES-DOM, which were effectively utilized during the IAHD process. The functional genes associated with nitrate-sulfide-organic carbon metabolism and electron transfer exhibited upregulation. The mixotrophic microbial community enables flexible adoption of multiple metabolic pathways. This strategy simultaneously achieves low-cost ES valorization and low-carbon nitrate/sulfide removal through integrated nitrogen-sulfur-carbon metabolism.

Strategy for repurposing waste anion exchange resins to construct a biofilter for removing dissolved organic matter: performance and mechanism

Anion exchange resins are widely employed in wastewater and drinking water treatment plants to remove dissolved organic matter (DOM). However, the degradation of resin performance necessitates the discontinuation of these treatment projects, resulting in the idling of underperforming resins, referred to as waste anion exchange resins (WAER). Given the substantial investment in operational costs, determining how to economically utilize WAER is essential for restarting the treatment projects. Therefore, this study proposed a strategy for repurposing WAER to construct a biofilter for DOM removal. A biofilter, termed biological anion exchange resin (BAER), was developed using WAER and compared with two conventional biofilters: biological activated carbon (BAC) and sand filter. After the acclimatization period, the BAER biofilter achieved a removal of up to 21.42 % of dissolved organic carbon (DOC), which is 5.8 times greater than the removal rate of the sand filter and comparable to the BAC. Notably, BAER exhibited the highest removal rate of aromatics, achieving 41.04 % UV254 removal, which are precursors to disinfection byproducts (DBPs). Consequently, BAER demonstrated superior control of DBPs, with a removal efficiency of 39.59 %. Additionally, BAER demonstrated effective removal of humic substances due to the bioregeneration of its adsorption sites, which led to significant differences in both the structural composition and functional expression of the biological community in BAER compared to other biofilters. This study also revealed that the bioregenerated adsorption sites primarily capture DOM through electrostatic attraction rather than ion exchange. Overall, these findings confirm the promising application of the BAER biofilter constructed with WAER and offer valuable insights into the associated removal processes.

The nexus between aeration intensity and organic carbon capture in contact-stabilization process: Insights from molecular structure transition of dissolved organic matters

Traditional energy-intensive pollution control pattern poses great challenges to the sustainable development of urban cities, necessitating the implementation of more compact and cost-effective biological treatment technology. High-rate contact stabilization (HiCS) process can effectively capture low-concentration organic carbon matters from municipal wastewater. However, the role of dissolved oxygen (DO) concentration at stabilization phase-a critical determinant of carbon capture efficiency-remains poorly understood, thus hindering its operation optimization and application. This work investigated the impact of DO content at the stabilization phase on the effluent quality and carbon capture efficiency of HiCS process from the perspectives of sludge dissolved organic matter (DOM) composition and microbial metabolism activity changes. The results showed that optimal carbon capture efficiency (52.1 %) and the lowest effluent chemical oxygen demand concentration were achieved at a DO concentration of 1 mg/L. Elevated DO levels would increase the aromaticity of DOM in sludge, rendering it more recalcitrant to microbial degradation. In addition, higher DO concentration induced a metabolic shift towards endogenous respiration among the microbial community, leading to the increased release of DOM and microbial metabolites, which in turn deteriorated the effluent quality. The findings of this work highlight the necessity of controlling appropriate aeration intensity when applying HiCS in practical application, to both effectively minimize organic carbon mineralization and operational energy consumption while without sacrificing pollutant removal performance.

New insight into the spatio-temporal patterns of functional groups of hotspot inside the composting aggregates by synchrotron-based FTIR in hyperthermophilic composting

Hyperthermophilic composting (HTC) is a recently developed and highly promising organic fraction of municipal solid waste (OFMSW) treatment technology. Investigation of organic matter (OM) dynamics in compost particle is thus crucial for the understanding of humification of HTC process. Herein, this work aimed to study the chemical and structural changes of OM at the molecular level during HTC of OFMSW using EEM and SR-FTIR analyses. Additionally, two-dimensional correlation spectroscopy (2D-COS) was also utilized to probe and identify the changes in chemical constituents and functional groups of organic compounds on the surface of compost particles during different composting periods. Results show that SR-FTIR can detect fine-scale (~μm) changes in functional groups from the edges to the interior of compost particles during different composting periods by mapping the particles in situ. In the hyperthermophilic stage (day 9), the extracted μ-FTIR spectrum reveals a distinct boundary between anaerobic and aerobic regions within the compost particle, with a thickness of anaerobic zone (1460 cm-1) of approximately 30 μm inside the particle's core. This provides direct evidence of anaerobic trends at compost microscales level within compost particles. 2D-COS analysis indicated that organic functional groups gradually agglomerated in the order of 1330 > 2930 > 3320 > 1600 > 1030 > 895 cm-1 to the core skeleton of cellulose degradation residues, forming compost aggregates with well physicochemical properties. Overall, the first combination of SR-FTIR and EEM provides complementary explanations for the humification mechanism of HTC, potentially introducing a novel methodology for investigating the environmental behaviors and fates of various organic contaminants associated with OM during the in-situ composting biochemical process.

Capabilities of Microbial Consortia from Disparate Environment Matrices in the Decomposition of Nature Organic Matter by Biofiltration

Dissolved organic matter (DOM) plays a pivotal role in drinking water treatment, influencing the performance of unit processes and final water quality (e.g. disinfection byproduct risk). Biofiltration is an effective method of reducing DOM, but currently lacks a comprehensive appreciation of the association between microbial profiles and biofiltration performance. In this study, bench-scale biofiltration units inoculated with microbial consortia from river and soil matrices were operated successively for comparing their efficacy in terms of DOM removal. The results showed that biofiltration units receiving soil microbes were significantly superior (p < 0.05) to those receiving river inoculated microbes in terms of decomposing DOM recalcitrant fractions and reducing DBP formation potential, resulting in DOC and DBP precursor removals of up to 58.4 % and 87.9 %, respectively. Characterization of the taxonomic composition revealed that differences in the microbial assembly of the two biofilter groups were subject to deterministic rather than stochastic factors. Furthermore, more complicated interspecific relationships and niche structures in soil inoculated biofilters were deciphered by co-occurrence network, providing a plausible profile on a taxonomic division of labor in DOM stepwise degradation. Accordingly, the contribution of microbial compositions was found to be of greater importance than the GAC mass and biomass attached to the media. Thus, this study has advanced the understanding of microbial-mediated DOM decomposition in biofiltration, and also provided a promising strategy for enhancing the process for water use via developing appropriate engineered consortia of bacteria.

Coagulation pretreatment coupled with indigenous microalgal-bacterial consortium system for on-site treatment of rural black wastewater

Improper treatment of rural black wastewater (RBW) presents substantial challenges, including the wastage of resource, environmental contamination, and economic consequences. This study proposed an integrated process for RBW treatment, consisting of coagulation/flocculation (C/F) pretreatment and subsequent inoculation of indigenous microalgal-bacterial consortium (IMBC) for nitrogen recovery, namely C/F-IMBC process. Specifically, the optimal C/F conditions (polyaluminium chloride of 4 g/l, polyacrylamide of 50 mg/l, and pH of 6) were determined through a series of single-factor experiments, considering CN, turbidity, and dissolved organic matter (DOM) removal, economic cost, and potential influence on the water environment. Compared to the sole IMBC system for RBW treatment, the proposed C/F-IMBC process exhibited a remarkable 1.23-fold increase in microalgal growth and a substantial 17.6-22.6 % boost in nitrogen recovery. The altered RBW characteristic induced by C/F pretreatment was supposed to be responsible for the improved system performance. In particular, the abundance of DOM was decreased and its composition was simplified after C/F pretreatment, based on the analysis for excitation-emission matrices with parallel factor and gas chromatography-mass spectrometry, thus eliminating the potential impacts of toxic DOM components (e.g., Bis(2-ethylhexyl) phthalate) on IMBC activity. It should also be noted that C/F pretreatment modified microbial community structure as well, thereby regulating the expression of nitrogen-related genes and enhancing the system nitrogen recovery capacity. For instance, the functional Cyanobacteria responsible for nutrient recovery was enriched by 1.95-fold and genes involved in the assimilatory nitrate reduction to ammonia pathway were increased by 1.52-fold. These fundamental findings are expected to offer insights into the improvement of DOM removal and nitrogen recovery for IMBC-based wastewater treatment system, and provide valuable guidance for the development of sustainable on-site RBW treatment technologies.

Bubbleless aerated-biological activated carbon as a superior process for drinking water treatment in rural areas

Drinking water supply in rural areas remains a substantial challenge due to complex natural, technical and economic conditions. To provide safe and affordable drinking water to all, as targeted in the UN Sustainable Development Goals (2030 Agenda), low-cost, efficient water treatment processes suitable for rural areas need to be developed. In this study, a bubbleless aeration BAC (termed ABAC) process is proposed and evaluated, involving the incorporation of a hollow fiber membrane (HFM) assembly within a slow-rate BAC filter, to provide dissolved oxygen (DO) throughout the BAC filter and an increased DOM removal efficiency. The results showed that after a 210-day period of operation, the ABAC increased the DOC removal by 54%, and decreased the disinfection byproduct formation potential (DBPFP) by 41%, compared to a comparable BAC filter without aeration (termed NBAC). The elevated DO (> 4 mg/L) not only reduced secreted extracellular polymer, but also modified the microbial community with a stronger degradation ability. The HFM-based aeration showed comparable performance to 3 mg/L pre-ozonation, and the DOC removal efficiency was four times greater than that of a conventional coagulation process. The proposed ABAC treatment, with its various advantages (e.g., high stability, avoidance of chemicals, ease of operation and maintenance), is well-suited to be integrated as a prefabricated device, for decentralized drinking water systems in rural areas.