Effect of engineered environment on microbial community structure in biofilter and biofilm on reverse osmosis membrane

Comprehensive assessment of chlorination disinfection on microplastic-associated biofilms

Chlorination on microplastic (MP) biofilms was comprehensively investigated with respect to disinfection efficiency, morphology, and core microbiome. The experiments were performed under various conditions: i) MP particles; polypropylene (PP) and polystyrene (PS), ii) MP biofilms; Escherichia coli for single-species and river water microorganisms for multiple-species, iii) different chlorine concentrations, and iv) different chlorine exposure periods. As a result, chlorination effectively inactivated the MP biofilm microorganisms. The disinfection efficiency increased with increasing the free chlorination concentration and exposure periods for both single- and multiple-species MP biofilms. The multiple-species MP biofilms were inactivated 1.3-6.0 times less than single-species MP biofilms. In addition, the PP-MP biofilms were more vulnerable to chlorination than the PS-MP biofilms. Morphology analysis verified that chlorination detached most MP biofilms, while a small part still remained. Interestingly, chlorination strongly changed the biofilm microbiome on MPs; the relative abundance of some microbes increased after the chlorination, suggesting they could be regarded as chlorine-resistant bacteria. Some potential pathogens were also remained on the MP particles after the chlorination. Notably, chlorination was effective in inactivating the MP biofilms. Further research should be performed to evaluate the impacts of residual MP biofilms on the environment.

Approaches to mitigation of hydrogen sulfide during anaerobic digestion process - A review

Anaerobic digestion (AD) is the primary technology for energy production from wet biomass under a limited oxygen supply. Various wastes rich in organic content have been renowned for enhancing the process of biogas production. However, several other intermediate unwanted products such as hydrogen sulfide, ammonia, carbon dioxide, siloxanes and halogens have been generated during the process, which tends to lower the quality and quantity of the harvested biogas. The removal of hydrogen sulfide from wastewater, a potential substrate for anaerobic digestion, using various technologies is covered in this study. It is recommended that microaeration would increase the higher removal efficiency of hydrogen sulfide based on a number of benefits for the specific method. The process is primarily accomplished by dosing smaller amounts of oxygen in the digester, which increases the system's oxidizing capacity by rendering the sulfate reducing bacteria responsible for converting sulfate ions to hydrogen sulfide inactive. This paper reviews physicochemical and biological methods that have been in place to eliminate the effects of hydrogen sulfide from wastewater treated anaerobically and future direction to remove hydrogen sulfide from biogas produced.

Air Pollutants Removal Using Biofiltration Technique: A Challenge at the Frontiers of Sustainable Environment

Air pollution is a central problem faced by industries during the production process. The control of this pollution is essential for the environment and living organisms as it creates harmful effects. Biofiltration is a current pollution management strategy that concerns removing odor, volatile organic compounds (VOCs), and other pollutants from the air. Recently, this approach has earned vogue globally due to its low-cost and straightforward technique, effortless function, high reduction efficacy, less energy necessity, and residual consequences not needing additional remedy. There is a critical requirement to consider sustainable machinery to decrease the pollutants arising within air and water sources. For managing these different kinds of pollutant reductions, biofiltration techniques have been utilized. The contaminants are adsorbed upon the medium exterior and are metabolized to benign outcomes through immobilized microbes. Biofiltration-based designs have appeared advantageous in terminating dangerous pollutants from wastewater or contaminated air in recent years. Biofiltration uses the possibilities of microbial approaches (bacteria and fungi) to lessen the broad range of compounds and VOCs. In this review, we have discussed a general introduction based on biofiltration and the classification of air pollutants based on different sources. The history of biofiltration and other mechanisms used in biofiltration techniques have been discussed. Further, the crucial factors of biofilters that affect the performance of biofiltration techniques have been discussed in detail. Finally, we concluded the topic with current challenges and future prospects.

Promoting the granulation process of aerobic sludge via a sustainable strategy of effluent reflux in view of AHLs-mediated quorum sensing

Aerobic granular sludge (AGS) has excellent performance in wastewater treatment. However, the formation and mechanism of AGS by effluent reflux are not fully understood in sequential batch reactors (SBRs). In this study, two reactors were constructed, among which R1 was the control group, and the R2 reactor refluxed one-fourth of the supernatant of the effluent to the influent water. In the reactor of R2, the granules had better COD and TN removal efficiencies and resistance to external shocks, and AGS produced more extracellular polymeric substances (EPS). Analysis of microbial community indicated that AHLs-mediated microbes, denitrifying microbes, and EPS producers were enriched. At the same time, the correlation between 3OC6-HSL, C8-HSL, C12-HSL and PN was 0.89*, 0.94** and 0.92* respectively, the possible mechanism of enhanced granulation was mainly the promotion of AHLs by effluent reflux. Therefore, the effluent reflux strategy could be an innovative and sustainable strategy that validates the function of AHLs-mediated QS to accelerate aerobic sludge granulation and maintain its structural stability.

Effects of microbial inactivation approaches on quantity and properties of extracellular polymeric substances in the process of wastewater treatment and reclamation: A review

Microbial extracellular polymeric substances (EPS) have a profound role in various wastewater treatment and reclamation processes, in which a variety of technologies are used for disinfection and microbial growth inhibition. These treatment processes can induce significant changes in the quantity and properties of EPS, and altered EPS could further adversely affect the wastewater treatment and reclamation system, including membrane filtration, disinfection, and water distribution. To clarify the effects of microbial inactivation approaches on EPS, these effects were classified into four categories: (1) chemical reactions, (2) cell lysis, (3) changing EPS-producing metabolic processes, and (4) altering microbial community. Across these different effects, treatments with free chlorine, methylisothiazolone, TiO₂, and UV irradiation typically enhance EPS production. Among the residual microorganisms in EPS matrices after various microbial inactivation treatments, one of the most prominent is Mycobacterium. With respect to EPS properties, proteins and humic acids in EPS are usually more susceptible to treatment processes than polysaccharides. The affected EPS properties include changes in molecular weight, hydrophobicity, and adhesion ability. All of these changes can undermine wastewater treatment and reclamation processes. Therefore, effects on EPS quantity and properties should be considered during the application of microbial inactivation and growth inhibition techniques.

Enhancing ultrafiltration performance by gravity-driven up-flow slow biofilter pre-treatment to remove natural organic matters and biopolymer foulants

Membrane fouling by influent biopolymers, and the formation of surface biofilms, are major obstacles to the practical application of membrane technologies. Identifying reliable and sustainable pre-treatment methods for membrane filtration remains a considerable challenge and is the subject of continuing research study worldwide. Herein, the performance of a bench-scale gravity-driven up-flow slow biofilter (GUSB) as the pre-treatment for ultrafiltration to reduce membrane fouling is presented. Dissolved organic carbon (DOC) was shown efficiently removed by the GUSB (around 80%) when treating a natural water influent. More significantly, biopolymers, with molecular weight (MW) between 20 kDa and 100 kDa, were effectively removed (62.8% reduction) and this led to a lower rate of transmembrane pressure (TMP) development by the UF membrane. Microbial diversity analysis further unraveled the function of GUSB in shaping microbes to degrade biopolymers, contributing to lower accumulation and different distribution pattern of SMP on the membrane surface. Moreover, the biofilm formed on the membrane surface after the pre-treatment of GUSB was observed to have a relative porous structure compared to the control system, which can also affect the fouling development. Long-term operation of GUSB further revealed its robust performance in reducing both natural organic matters and UF fouling propensity. This study overall has demonstrated the potential advantages of applying a GUSB to enhance UF process performance by reducing biofouling and improving effluent quality.

Biological-based methods for the removal of volatile organic compounds (VOCs) and heavy metals

The current scenario of increased population and industrial advancement leads to the spoliation of freshwater and tapper of the quality of water. These results decrease in freshwater bodies near all of the areas. Besides, organic and inorganic compounds discharged from different sources into the available natural water bodies are the cause of pollution. The occurrence of heavy metals in water and volatile organic compounds (VOCs) in the air is responsible for a vast range of negative impacts on the atmosphere and human health. Nonetheless, high uses of heavy metals for human purposes may alter the biochemical and geochemical equilibrium. The major air contaminants which are released into the surroundings known as VOCs are produced through different kinds of sources, such as petrochemical and pharmaceutical industries. VOCs are known to cause various health hazards. VOCs are a pivotal group of chemicals that evaporate readily at room temperature. To get over this problem, biofiltration technology has been evolved for the treatment of heavy metals using biological entities such as plants, algae, fungi, and bacteria. Biofiltration technology is a beneficial and sustainable method for the elimination of toxic pollutants from the aquatic environment. Various types of biological technologies ranging from biotrickling filters to biofilters have been developed and they are cost-effective, simple to fabricate, and easy to perform. A significant advantage of this process is the pollutant that is transformed into biodegradable trashes which can decompose within an average time period, thus yielding no secondary pollutants. The aim of this article is to scrutinize the role of biofiltration in the removal of heavy metals in wastewater and VOCs and also to analyze the recent bioremediation technologies and methods.

Micro-particles as interfering substances in colorimetric residual chlorine measurement

Conventional methods using o-tolidine and N,N-diethyl-p-phenylenediamine as colorimetric reagents have been extensively applied worldwide in residual chlorine measurement for water quality and environmental management. Different types of interferences resulting in erroneous measurements while using colorimetry have been previously reported. In this study, we experimentally demonstrated micro-particles as interfering substances in selected inorganic (five metal oxidants) and organic (microalgae) particles. The results indicated erroneous measurements (viz. colour development) for three of the selected particles. These erroneous measurement levels were evaluated with reference to the chlorine concentration (in mg-Cl₂/L, hereafter represented as mg/L) in relation to both representative colorimetric reagents in terms of the amount of particles and time variations. A novel viewpoint that filtration could be a possible solution to the erroneous measurement caused by such micro-particles was proposed.

Styrene removal with an acidic biofilter with four packing materials: Performance and fungal bioaerosol emissions

The packing material used in acidic biofilters (ABFs) has a significant impact on styrene removal. The bioaerosol emission was rarely considered when evaluating the packing materials in the ABFs. Four ABFs packed with ceramsite, compost, lava and polyurethane (PU) were developed and compared for their styrene removal and fungal bioaerosol emissions characteristics over 529 days. The removal efficiencies of styrene in the ABFs were higher under the condition of longer empty bed residence time (EBRT) and lower inlet concentration. The maximum styrene elimination capacities of the ABFs with ceramsite, compost, lava and PU were 74.57, 87.81, 67.13 and 101.88 g/m³ h, respectively. A lower pressure drop and the highest fungi count were observed in the ABF packed with PU. The emissions concentrations of fungal bioaerosols at the humidity of 63.5% were lower than those at a humidity of 42.7% and it increased with the air velocity. Additionally, the concentrations of fungal bioaerosols emitted from the ABFs packed with PU were 2168 ± 145-3661 ± 257 CFU/m³, which was 33%-90% lower than those of the other three ABFs. The particle size distributions of the fungal bioaerosols emitted from the ABFs packed with PU and compost were mainly centered around large particles. Considering the removal of styrene and the fungal bioaerosols emissions, PU was the optimal packing material for ABF.

Effect of granular activated carbon pore-size distribution on biological activated carbon filter performance

Proper granular activated carbon (GAC) selection could improve the performance of biological activated carbon (BAC) filters through a combination of adsorption and biodegradation, while the GACs used in BAC filters are now mainly selected according to adsorption function, ignoring biodegradation. In this study, sand filter effluent obtained from a drinking water treatment plant was fed into continuous-flow bench-scale BAC columns operated in parallel over 245 days to examine the effects of GAC pore-size distribution on BAC filter performance, in terms of the dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors. A metagenomic analysis indicated that bacterial community structure played an important role in BAC filter performance. A significant correlation was found between metabolism-related proteins and the volume of micro-level macropores based on metaproteomic analysis. It is suggested that the adsorption saturation was dynamic and that adsorption played a role in the performance of the BAC filters throughout the 245-day operating period. Renewed adsorption capacity, or bioregeneration, was driven by bacterial metabolic activity. Such activity largely depended on the organic matter adsorbed by the GAC, in which micro-level macropores, especially those with diameters of 0.2-10 μm, played an important but previously unrecognized role. The results suggest that more attention should be paid to well-developed pores and pore-size distribution in the production and selection of GAC used for full-scale drinking water biofilters.

Biodiversity and ecology of microorganisms in high pressure membrane filtration systems

High-pressure membrane filtration (reverse osmosis and nanofiltration) is used to purify different water sources, including wastewater, surface water, groundwater and seawater. A major concern in membrane filtration is the accumulation and growth of micro-organisms and their secreted polymeric substances, leading to reduced membrane performance and membrane biofouling. The fundamental understanding of membrane biofouling is limited despite years of research, as the means of microbial interactions and response to the conditions on the membrane surface are complicated. Here, we discuss studies that investigated the microbial diversity of fouled high-pressure membranes. High-throughput amplicon sequencing of the 16S rRNA gene have shown that Burkholderiales, Pseudomonadales, Rhizobiales, Sphingomonadales and Xanthomonadales frequently obtain a high relative abundance on fouled membranes. The bacterial communities present in the diverse feed water types and in pre-treatment compartments are different from the communities on the membrane, because high-pressure membrane filtration provides a selective environment for certain bacterial groups. The biofilms that form within the pre-treatment compartments do not commonly serve as an inoculum for the subsequent high-pressure membranes. Besides bacteria also fungi are detected in the water treatment compartments. In contrast to bacteria, the fungal community does not change much throughout membrane cleaning. The stable fungal diversity indicates that they are more significant in membrane biofouling than previously thought. By reviewing the biodiversity and ecology of microbes in the whole high pressure membrane filtration water chain, we have been able to identify potentials to improve biofouling control. These include modulation of hydrodynamic conditions, nutrient limitation and the combination of cleaning agents to target the entire membrane microbiome.

Reduction of biofouling potential in cartridge filter by using chlorine dioxide for enhancing anti-biofouling of seawater reverse osmosis membrane

In general, cartridge filters (CFs) are installed before reverse osmosis systems as a safeguard to minimize fouling of the reverse osmosis membrane in seawater desalination plants. Depending on the retention time of microorganisms and various fouling matter in the storage tank, pipe, and filter housing, serious fouling of the CF may occur, decreasing its lifetime. More importantly, biofouling of CFs in a continuous process can have a significant impact on reverse osmosis membrane fouling. Few studies related to CF fouling and control have been undertaken due to the low cost of CFs. Herein, comparative evaluation of optical density (O.D) for Cl₂ and ClO₂ was performed to investigate the efficiency of biofouling control and for developing alternative disinfection processes because the chemistry and reactivity of ClO₂ differ from those of Cl₂. The results showed that the concentrations of Cl₂ and ClO₂ required to achieve a log reduction value of 2 for the live bacterial cells with 180 min of contact time were 1.5 and 0.6 mg L^-1, respectively. Both Cl₂ and ClO₂ were effective for the control of organic matter and particles. However, the required Cl₂ concentration (1.5 mg L^-1) was 2.5 times higher than that of ClO₂ (0.6 mg L^-1). Surface analysis and economic evaluation of the CF showed that ClO₂ has higher biofouling control ability than Cl₂ and is more economical, at a current cost of $ 23,667 during seawater desalination plant duration.

Process stability and comparative rDNA/rRNA community analyses in an anaerobic membrane bioreactor with silicon carbide ceramic membrane applications

This study evaluated the feasibility of using a silicon carbide (SiC) anaerobic ceramic membrane bioreactor (AnCMBR) to co-manage domestic wastewater (DWW) and food waste recycling wastewater (FRW). A pilot-scale SiC-AnCMBR was put into operation for 140 days under two different organic loading rates (OLRs): 5 kg COD m^-3 d^-1 (OLR 5) and 3 kg COD m^-3 d^-1 (OLR 3). The organic removal efficiency was 93.5 ± 3.7% over the operational period. Methane production increased significantly after sludge re-seeding at OLR 3. rDNA and rRNA microbial results showed that the active archaeal community was affected by sludge re-seeding, whereas the active bacterial community was not, indicating that a shift in the active archaeal community was responsible for the increased methane production. Our results thus suggest that SiC-AnCMBRs are a promising option for co-managing DWW and FRW.

Sunlight caused interference in outdoor N, N-diethyl-p-phenylenediamine colorimetric measurement for residual chlorine and the solution for on-site work

Chlorination is the most common method to control water qualities, in some case on-site outdoor measurements are required to measure easily-decaying residual chlorine concentration appropriately without delay. In this study sunlight-induced unexpected colour development (UCD) of N, N-diethyl-p-phenylenediamine (DPD) colorimetric measurement was studied under several sun exposure conditions. The colour development level was evaluated with reference to chlorine concentration (mg/L) and relationships between colour development rate (mg/L min) and intensities of solar were investigated. UCD was found to be related to both exposure intensity and time. By means of exposure experiment under specific wavelength of ultraviolet (UV), it was confirmed that both middle and short wavelength of UV radiation being responsible for such an unexpected measurement. Consequently, a simple device was designed using three commercially available anti-UV films, one of which could effectively prevent the UCD from direct sun exposure.

Negligible seeding source effect on the final ANAMMOX community under steady and high nitrogen loading rate after enrichment using poly(vinyl alcohol) gel carriers

This study investigated the effect of seeding source on the mature anaerobic ammonia oxidation (ANAMMOX) bacterial community niche in continuous poly(vinyl alcohol) (PVA) gel systems operated under high nitrogen loading rate (NLR) condition. Four identical column reactors packed with PVA gels were operated for 182 d using different seeding sources which had distinct community structures. The ANAMMOX reaction was achieved in all the bioreactors with comparable total and ANAMMOX bacterial 16S rRNA gene quantities. The bacterial community structure of the bioreactors became similar during operation; some major bacteria were commonly found. Interestingly, one ANAMMOX species, "Candidatus Brocadia sinica", was conclusively predominant in all the bioreactors, even though different seeding sludges were used as inoculum source, possibly due to the unique physiological characteristics of "Ca. Brocadia sinica" and the operating conditions (i.e., PVA gel-based continuous system and 1.0 kg-N/(m³·d) of NLR). The results clearly suggest that high NLR condition is a more significant factor determining the final ANAMMOX community niche than is the type of seeding source.

Effects of changes in temperature on treatment performance and energy recovery at mainstream anaerobic ceramic membrane bioreactor for food waste recycling wastewater treatment

An anaerobic ceramic membrane bioreactor (AnCMBR) has been attracted as an alternative technology to co-manage various organic substrates. This AnCMBR study investigated process performance and microbial community structure at decreasing temperatures to evaluate the potential of AnCMBR treatment for co-managing domestic wastewater (DWW) and food waste-recycling wastewater (FRW). As a result, the water flux (≥6.9 LMH) and organic removal efficiency (≥98.0%) were maintained above 25 °C. The trend of methane production in the AnCMBR was similar except for at 15 °C. At 15 °C, the archaeal community structure did not shifted, whereas the bacterial community structure was changed. Various major archaeal species were identified as the mesophilic methanogens which unable to grow at 15 °C. Our results suggest that the AnCMBR can be applied to co-manage DWW and FRW above 20 °C. Future improvements including psychrophilic methanogen inoculation and process optimization would make co-manage DWW and FRW at lower temperature climates.