Biological Wastewater Treatment Systems Research Articles

Microbial Ecology of Granular Biofilm Technologies for Wastewater Treatment: A Review.

Nowadays, the discharge of wastewater is a global concern due to the damage caused to human and environmental health. Wastewater treatment has progressed to provide environmentally and economically sustainable technologies. The biological treatment of wastewater is one of the fundamental bases of this field, and the employment of new technologies based on granular biofilm systems is demonstrating success in tackling the environmental issues derived from the discharge of wastewater. The granular-conforming microorganisms must be evaluated as functional entities because their activities and functions for removing pollutants are interconnected with the surrounding microbiota. The deep knowledge of microbial communities allows for the improvement in system operation, as the proliferation of microorganisms in charge of metabolic roles could be modified by adjustments to operational conditions. This is why engineering must consider the intrinsic microbiological aspects of biological wastewater treatment systems to obtain the most effective performance. This review provides an extensive view of the microbial ecology of biological wastewater treatment technologies based on granular biofilms for mitigating water pollution.

Magnetite alleviating calcification of anaerobic granular sludge (AnGS): Electron transfer enhancement and ion competition

Calcification accompanied by deactivation of anaerobic granular sludge (AnGS) is a continuing challenge for high calcium wastewater treatment. The interaction between Ca2+ and extracellular polymeric substances (EPS) is a precondition for this problem. In this study, magnetite for activity recovery and calcification alleviation simultaneously of AnGS under high calcium stress was investigated. The results showed that, in the presence of magnetite, the relative biogas production increased by 13.2 % with the higher activities of key enzymes involved in methanogenesis. Methanosarcina turned into the dominant methanogens, and syntrophic bacteria such as Chloroflexi, Synergistota were enriched, which indicated the enhancement of electron transfer by magnetite, supported by an 18 % increase of the electron transfer system (ETS) activity. Further characterizations of AnGS suggested that the granule calcification was alleviated with a final decrease of 13–40 % calcium content of AnGS with particle size of 1–2.5 mm. Besides, calcium was partially substituted by iron in the EPS, and the secretion of EPS especially proteins decreased. Batch tests demonstrated the competition between Fe2+ dissolved from magnetite and Ca2+, which interfered the interaction between Ca2+ and EPS, so the granule calcification was prevented. Therefore, magnetite played a pluripotent role in the alleviation of granule calcification and deactivation in situ via (1) enhancing electron transfer, and (2) blocking the complex between Ca2+ and EPS. This study provides a novel insight into the application of conductive metal materials in biological wastewater treatment systems suffering from high calcium attack.

Bioengineering Comamonas testosteroni CNB-1: a robust whole-cell biocatalyst for efficient PET microplastic degradation

The escalating crisis of polyethylene terephthalate (PET) microplastic contamination in biological wastewater treatment systems is a pressing environmental concern. These microplastics inevitably accumulate in sewage sludge due to the absence of effective removal technologies. Addressing this urgent issue, this study introduces a novel approach using DuraPETase, a potent enzyme with enhanced PET hydrolytic activity at ambient temperatures. Remarkably, this enzyme was successfully secreted from Comamonas testosteroni CNB-1, a dominant species in the active sludge. The secreted DuraPETase showed significant hydrolytic activity toward p-NPB and PET nanoplastics. Furthermore, the CNB-1 derived whole-cell biocatalyst was able to depolymerize PET microplastics under ambient temperature, achieving a degradation efficiency of 9% within 7 days. The CNB-1-based whole biocatalysts were also capable of utilizing PET degradation intermediates, such as terephthalic acid (TPA) and ethylene glycol (EG), and bis(2-hydroxyethyl)-TPA (BHET), for growth. This indicates that it can completely mineralize PET, as opposed to merely breaking it down into smaller molecules. This research highlights the potential of activated sludge as a potent source for insitu microplastic removal.Graphical

Upcycling of used ceramic membrane as media in upflow biological reactor treating low strength wastewater

This work investigates the feasibility of media prepared from used (fouled) ceramic membrane (CM) in an upflow biological reactor (UBR) treating synthetic low strength wastewater (chemical oxygen demand, COD ∼ 200 mg/L) representative of an urban drain. The UBR was operated over 163 days at different hydraulic retention times (HRTs) of 48 h, 36 h, 24 h, 12 h and 6 h with corresponding upflow velocity between 0.06 m/d and 0.45 m/d. The COD removal was comparable at HRTs between 48 h and 12 h i.e., 83.4 ± 5.2 % (48 h), 80.5 ± 7.5 % (24 h), 76.2 ± 6.7 % (36 h) and 84.7 ± 7.2 % (12 h), followed by a marginal drop at 6 h HRT (69.9 ± 5.6 %). Ammonia removal was observed at HRTs of 48 h (37.6 ± 24.3 %) and 36 h (50.1 ± 20 %) only. Phosphate followed the same trend with removal observed at higher HRTs alone: 48 h (28.9 ± 12.5 %), 36 h (33.2 ± 8.7 %) and 24 h (23 ± 26.8 %). Total suspended solids (TSS) in the treated effluent was the lowest at 12 h HRT (6.2 mg/L). Only ∼ 3 % reduction in media porosity was observed after 163 days of operation. Overall, this media showed the recycling potential of fouled CM in a biological wastewater treatment system.

Metagenomics and metatranscriptomics suggest pathways of 3-chloroaniline degradation in wastewater reactors

Biological wastewater treatment systems are often affected by shifts in influent quality, including the input of toxic chemicals. Yet the mechanisms underlying the adaptation of activated sludge process performance are rarely studied in a controlled and replicated experimental setting, particularly when challenged with a sustained toxin input. Three replicate bench-scale bioreactors were subjected to a chemical disturbance in the form of 3-chloroaniline (3-CA) over 132 days, after an acclimation period of 58 days, while three control reactors received no 3-CA input. Ammonia oxidation was initially affected by 3-CA. Within three weeks of the experiment, microbial communities in all three treatment reactors adapted to biologically degrade 3-CA resulting in partial ammonia oxidation recovery. Combining process and microbial community data from amplicon sequencing with potential functions gleaned from assembled metagenomics and metatranscriptomics data, two putative degradation pathways for 3-CA were identified. The first pathway, determined from metagenomics data, involves a benzoate dioxygenase and subsequent meta-cleavage of the aromatic ring. The second, determined from intensive short-term sampling for gene expression data in tandem with 3-CA degradation, involves a phenol monooxygenase followed by ortho-cleavage of the aromatic ring. The relative abundances of amplicon sequence variants associated with the genera Gemmatimonas, OLB8, and Taibaiella correlated significantly with 3-CA degradation. Metagenome-assembled genome data also showed the genus OLB8 to be differentially enriched in treatment reactors, making it a strong candidate as 3-CA degrader. Using replicated reactors, this study has demonstrated the impact of a sustained stress on the activated sludge process. The unique and novel features of this study include the identification of putative pathways and potential degraders of 3-CA using long-term and short-term sampling in tandem with multiple methods in a controlled and replicated experiment.

Microbiological assessment of wastewater of milk processing enterprise

Recently, microbiological methods of wastewater treatment have been increasingly used. Microbiological destruction of a wide range of polycarbon organic compounds occurs due to the formation of a microbial sequence. The sequence consists in the fact that the end products (exometabolites) of “primary” destructive microorganisms are the primary substrates for “secondary” destructive microorganisms. The purpose of the work was to conduct a microbiological assessment of industrial wastewater from the fi ltration pond of a dairy processing enterprise using a biological purifi cation system. The proposed concept is a spatial sequence for the treatment of wastewater containing a wide range of organic substances of high concentration. The essence of the biological purifi cation system was the introduction of microbiological preparations into wastewater according to an individually developed technology. At the same time, air was additionally injected into the water column by an aerator. Wastewater sampling was carried out in accordance with the general requirements for surface waters according to National State Standard 31861-2012. Sample preparation and research were carried out using standard techniques. The wastewater of milk processing enterprises contains a signifi cant amount of proteins. During the decomposition of the protein the process of ammonifi cation occurs, i.e. the splitting of amino groups and their accumulation in the medium in the form of NH4 or NH3, these compounds alkalize the medium, which explains the increase in pH. The conducted sanitary and microbiological studies of wastewater and biofi lm using a biological wastewater treatment system of the milk processing enterprise indicate that a decrease in the concentration of organic matter is a consequence of the positive redox potential of the medium. The increased value of the redox potential means the decrease in the concentration of organic compounds in wastewater, which is an indicator of the effectiveness of treatment.

Impact of Dissolved Oxygen on the Performance and Microbial Dynamics in Side-Stream Activated Sludge Hydrolysis Process

Dissolved oxygen (DO) plays an important role in the performance of biological wastewater treatment systems. This study investigated the effect of the DO concentration on nutrient removal performance and microbial community structure in side-stream activated sludge hydrolysis (SSH) and conventional anaerobic/anoxic/aerobic (A2O) processes. The results showed that the change in DO had little effect on the removal performance of chemical oxygen demand (COD), and the removal efficiencies were about 90% for both reactors. Compared with the high DO level (4.1–6.9 mg/L), the A2O and SSH reactors had better nitrogen removal performance at low (0.5–2.2 mg/L) and moderate (2.2–3.9 mg/L) DO levels, with ammonia (NH4+-N) removal efficiencies of 88–89% and 89–91%, respectively, and total nitrogen (TN) removal efficiencies of 74–76% and 75–81%, respectively. Directly reducing the DO concentration from high to low reduced the phosphate removal efficiencies of the A2O and SSH reactors from 80.2% and 86.2% to 63.1% and 70.6%, respectively, while re-elevating the DO concentration to moderate levels significantly improved the phosphate removal efficiencies to 94.6% and 96.0%, respectively. Compared to the A2O reactor, the SSH reactor had more stable and better nutrient removal performance under different DO conditions, partly due to the additional carbon sources produced through the sludge fermentation in the side-stream reactor. The decrease in the DO concentration resulted in a decrease in the relative abundance of Acinetobacter but an increase in the relative abundance of Competibacter, potentially leading to the deterioration in phosphorus removal.

A Review of Rotating Biological Contactors for Wastewater Treatment

A rotating biological contactor (RBC) is a type of attached-growth biological wastewater treatment system and a widely used biological wastewater treatment technology. It employs a series of rotating discs to support microbial growth and promote the removal of pollutants from wastewater. RBC is widely recognized for its simplicity of design, high reliability, and low energy consumption. It has been used in various applications, from small-scale decentralized systems to large municipal wastewater treatment plants. The current review provides an overview of RBC bioreactors, design parameters, and the factors that influence biological performance, such as hydraulic retention time, sludge retention time, organic loading rate, disc rotational speed, and temperature. The review also highlights the advantages and disadvantages of RBCs compared with other wastewater treatment technologies and discusses their role in sustainable environmental performance. The future prospects of RBC are also discussed, including integration with other technologies, such as membrane filtration and potential use in resource recovery. The review explores the application of RBC in decentralized wastewater treatment and the potential to provide sustainable solutions for wastewater management in rural and remote areas. Overall, RBC remains a promising option for effective and efficient wastewater treatment, particularly in situations where simplicity, reliability, and low energy consumption are desired.

Multichannel Biolayer Interferometry to Probe the Binding of Microbial Extracellular Polymeric Substances to Sulfamethoxazole

Microbial extracellular polymeric substances (EPS) can bind to sulfonamides, influencing the removal of antibiotics in biological wastewater treatment systems. However, information about the binding kinetics and affinities of EPS for sulfonamides remains unavailable due to the lack of an effective approach. In this study, biolayer interferometry (BLI), a multichannel sensing technique, is first established to probe the binding of the antibiotic sulfamethoxazole (SMX) to microbial EPS. The influence of environmental conditions, such as pH, ionic strength, and temperature, on this binding interaction is investigated. The results indicate that multichannel BLI can rapidly and accurately determine the association/dissociation rate constants and binding affinities of the binding interactions between EPS and SMX. The high reproducibility of the sensorgrams demonstrates the reliability of the BLI approach. Via comparison of the obtained parameters, the binding interactions between EPS and SMX are significantly improved under acidic conditions compared to those under neutral or alkaline conditions. A higher ionic strength and a lower temperature yield stronger binding between EPS and SMX. BLI analysis allows multichannel operations concurrently, substantially reducing the testing time. The BLI approach developed in this study provides a powerful tool for probing the binding interactions between complex environmental samples.

Quantification of hydrolysis activity in a biological wastewater treatment context

This paper reviews currently available methods for hydrolysis activity monitoring of the most commonly encountered enzyme categories in biological wastewater treatment. While highlighting the relevant methods for protein, lipid, carbohydrate, organic phosphate, and ester hydrolysis, the discussion of their pros and cons is predominantly aimed at revealing the relevance of the to-be-hydrolyzed substrates that are used in the methods. These "substrates" should mimic the proteins, lipids, or other polymers that are present in the wastewater and are in the reviewed methods (i) real substrates (i.e., naturally present in the wastewater), (ii) chromogenic substrates, or (iii) fluorogenic substrates. We conclude that exploiting relevant substrates such as casein or starch, containing fluorophores, has the highest potential for meaningful high throughput hydrolysis quantification and that lipase activity monitoring is still cumbersome. Monitoring the hydrolysis activity in biological wastewater treatment systems is an underdeveloped area. With this review, which aims at providing a condensed and practice-oriented overview, we hope to facilitate the start or continuation of such monitoring. This monitoring will only grow in importance, given the transition from wastewater treatment plants towards water resource recovery facilities. KEY POINTS: • Colorimetric-based methods are vulnerable to sludge matrix interference. • Bonds in p-nitrophenol-based methods are not representative for the targeted substrates. • Direct methods with relevant/real substrates are preferred. • Fluorophore-containing (real) substrates enable high throughput screening.

Phylogenetic group-based assembly and co-occurrence pattern of the microbial community in full-scale wastewater treatment plants during the Chinese spring festival

The quality and quantity of domestic sewage discharge vary significantly during the Chinese Spring Festival due to the huge population shift. The dynamics of microbial community traits during the Spring Festival, particularly the phylogenetic group-based assembly and co-occurrence patterns, are however little understood. Here, influent and activated sludge samples from 2 full-scale wastewater treatment plants were collected bi-daily throughout a 20-day Spring Festival period and subjected to high-throughput Illumina-MiSeq sequencing. The findings revealed that the microbial communities in the activated sludge displayed a comparatively stable pattern, and that the influent communities experienced significant temporal fluctuations in terms of diversity and composition. The characterization by “Infer Community Assembly Mechanisms by Phylogenetic-bin based null model” demonstrated that for Competibacter glycogen-accumulating organisms, the assembly mechanism shifted from deterministic process (HoS = 69.5%) before the Spring Festival to stochastic process (DR = 65.9%) after the Spring Festival. The network analysis revealed that the network structure of sludge communities was more stable before the Spring Festival than that after the Spring Festival. Additionally, sludge communities had no keystone species in common with the influent before the Spring Festival, while the sludge and influent communities shared two keystone taxa after the Spring Festival (Sebaldella and Candidatus Competibacter). This study would deepen our understanding of the microbial ecology in biological wastewater treatment systems, which also aids in managing wastewater treatment plants.

Antimony toxicity upon microorganisms from aerobic and anaerobic environments

Antimony (Sb) is a toxic and carcinogenic metalloid that can be present in contaminated water generated by mining operations and other industrial activities. The toxicity of Sb (III) and Sb (V) to aerobic microorganisms remains limited and unexplored for anaerobic microorganisms involved in hydrogen (H2) and methane (CH4) production. This study aimed to evaluate the toxicity of Sb (III) and Sb (V) upon aerobic and anaerobic microorganisms important in biological wastewater treatment systems. Sb (III) was more toxic than Sb (V) independently of the test and environment evaluated. Under aerobic conditions maintained in the Microtox assay, Sb (V) was not toxic to Allivibrio fischeri at concentrations as high as 500 mg/L, whereas Sb (III) caused just over 50% inhibition at concentration of 250 mg/L after 5 min of exposure. In the respirometry test, for the specific oxygen uptake rate, the concentrations of Sb (III) and Sb (V) displaying 50% inhibition were 0.09 and 56.2 mg/L, respectively. Under anaerobic conditions, exposure to Sb (III) and Sb (V) led to a decrease in microorganisms activity of fermentative and methanogenic processes. The results confirm that the microbial toxicity of Sb depends on its speciation and Sb (III) displays a significantly higher inhibitory potential than Sb (V) in both aerobic and anaerobic environments.

Effects of bioaugmentation on the performance of industrial-scale activated sludge sequencing batch reactor under load shock of heavy oil refinery wastewater

The stable and efficient operation of the cyclic activated sludge sequencing batch reactor (CASSBR) in heavy oil refineries has become an urgent necessity in wastewater biotreatment. Here, the present study focuses on the selection of inoculated strains, the optimization of process parameters, and the effects of bioaugmentation on the performance in CASSBR under the different rates of heavy oil refinery wastewater shock loading. Results showed that the shock resistance of the CASSBR gradually enhanced and the normal performance was restored in a short time by the addition of a 0.1% biofortifier, and the average removal efficiency of chemical oxygen demand and total nitrogen reached 86% and 55% within 15 days, respectively. The recovery time of the reactor was shortened to 6 days by bioaugmentation measures. This study not only presents a detailed case on the ecological trade-off of the bioreactor and pollutant removal of inoculated strains during bioaugmentation, but also provides a theoretical basis and technical support for evaluating the effects of heavy oil refinery wastewater shock loading on biological wastewater treatment systems.

Microbial Population Dynamics in Lemnaceae (Duckweed)-Based Wastewater Treatment System.

The dynamic microflora associated within, and in the surrounding aquatic environment, has been found to be responsible for the functional properties of many aquatic plants. The aim of the current work was to evaluate the effectiveness of Lemnaceae-based wastewater treatment system under tropical conditions and investigate the changes in the aquatic microflora upon plant growth. A biological wastewater treatment system was designed and investigated using mixed Lemnaceae culture comprising Lemna minor and Spirodela polyrhiza in a batch mode. A significant reduction in total solids (31.8%), biochemical oxygen demand (93.5%), and chemical oxygen demand (73.2%) was observed after seven days of duckweed growth using a low inoculum. A preliminary study on the change in the microbial population diversity and functionality, in the wastewater before and after treatment, revealed an increase in the denitrifying microflora in wastewater post-Lemnaceae treatment. Dominance of 10 bacterial phyla, contributing for 98.3% of the total bacterial communities, was recorded, and ~ 50.6% loss of diversity post-treatment of wastewater was revealed by the Shannon Index. Among 16 bacterial families showing relative abundance of ≥ 1% in untreated wastewater, Methylobacteriaceae, Pseudomonadaceae, Brucellaceae, Rhodobacteraceae, and Acetobacteraceae prevailed in the water post-treatment by duckweeds. This is a novel work done on the dynamics of aquatic microflora associated with Lemnaceae under tropical Indian conditions. It confirms the application of Lemnaceae-based wastewater treatment system as effective biofilter and calls for further studies on the active involvement of the endophytic and aquatic microflora in the functions of these plant.

Review of Latest Advances in Nature-Inspired Algorithms for Optimization of Activated Sludge Processes

The activated sludge process (ASP) is the most widely used biological wastewater treatment system. Advances in research have led to the adoption of Artificial Intelligence (AI), in particular, Nature-Inspired Algorithm (NIA) techniques such as Genetic Algorithms (GAs) and Particle Swarm Optimization (PSO) to optimize treatment systems. This has aided in reducing the complexity and computational time of ASP modelling. This paper covers the latest NIAs used in ASP and discusses the advantages and limitations of each algorithm compared to more traditional algorithms that have been utilized over the last few decades. Algorithms were assessed based on whether they looked at real/ideal treatment plant (WWTP) data (and efficiency) and whether they outperformed the traditional algorithms in optimizing the ASP. While conventional algorithms such as Genetic Algorithms (GAs), Particle Swarm Optimization (PSO), and Ant Colony Optimization (ACO) were found to be successfully employed in optimization techniques, newer algorithms such as Whale Optimization Algorithm (WOA), Bat Algorithm (BA), and Intensive Weed Optimization Algorithm (IWO) achieved similar results in the optimization of the ASP, while also having certain unique advantages.

Removal of Clostridium perfringens and Staphylococcus spp. in Microalgal–Bacterial Systems: Influence of Microalgal Inoculum and CO2/O2 Addition

Conventional biological wastewater treatment systems have a low pathogen removal capacity. Microalgae-based systems are sustainable and low-cost alternatives for wastewater treatment and are capable of removing pathogens from domestic effluents. Other microorganisms have been identified as alternative indicators of disinfection since they have greater resistance than Escherichia coli, either because of the formation of spores or because of other mechanisms of protection, and because they spread in wastewater treatment plants; the most important are Clostridium perfringens and Staphylococcus spp. This study assessed the influence of microalgal strains (e.g., Chlorella vulgaris and Scenedesmus acutus Meyen) and the addition of CO2 and O2 on the removal of C. perfringens and Staphylococcus spp. from domestic wastewater in microalgal–bacterial systems. The removal of C. perfringens (2.5 to 3.2 log units) and Staphylococcus sp. (1.8 to 2.0 log units) was higher when using Chlorella sp. inoculum. The addition of CO2 and O2 did not have a significant effect on the removal of pathogenic bacteria. The main mechanism of C. perfringens removal was by means of toxins and bactericidal substances produced by the microalgae, while Staphylococcus spp. removal also occurred through photooxidative processes.

Performance Prediction of the Full-Scale KNR Biological Nutrient Removal Process Using Multivariate Dynamic Process Model with the Grammar-Based Genetic Programming (GBGP) System

Biological wastewater treatment systems are characterized by large temporal variability of inflow, variable concentrations of components in the incoming wastewater to the plant, and highly variable biological reactions within the process. This paper proposes an automatic process model induction system using an evolutionary computional intelligence, called grammar-based genetic programming (GBGP), that is specially designed to automatically discover multivariate dynamic process models that best fit observed process data. This automatic process model induction system combines an evolutionary self-organizing system of genetic programming paradigm with various mathematical functions for a multivariate nonlinear model evolution using a grammar system via the mechanism of genetics and natural selection. In the GBGP, a four-step modelling procedure was performed: (1) initialization: generatr an initial population of P models using contex-free grammar. generation K=0; (2) optimize each model (variables and constants) in the population; (3) execute and evaluate the fitness of each model in the population; (4) genetic loop: repeat until termination criterion is met (maximum generation Kmax). The results demonstrate that the multivariate dynamic process modelling technique presented using a grammar-based genetic programming (GBGP) provides a valuable tool for predicting the out puts with high levels of accuracy and identifying key operating variables for the full-scale KNR biological nutrient removal process. These modells are derived automatically in the form of understandable mathematical formulas that enable engineers to extract important knowledge hidden in the data and develop better operation and control strategies.

Toxic Effects of Xenobiotic Compounds on the Microbial Community of Activated Sludge

AbstractThe presence of xenobiotic compounds in biological wastewater treatment processes with activated sludge may reduce microbial communities, disrupt microbial diversity, and diminish system performance. Shock loads and unusual operating events in these biological systems have negative impacts on their efficiency and reliability for pollutant degradation, thereby posing high risk to microorganisms and water quality of receiving treated water bodies. The severity and characteristics of the occurring damage are determined by the toxic contaminant's degree, nature and mode of application. This review highlights the effects of metabolic uncouplers, heavy metals, carbon nanotubes, pharmaceuticals and personal care products, nanoparticles, and phenolic compounds stress on microbial biomass in activated sludge systems. The synergistic, antagonistic, and shock load toxic effects of hybrid substances exposure in an activated sludge sequential batch reactor (SBR) system on organic and nutrient removal, system efficiency, and toxicants biodegradation are discussed. The findings can be used to provide a theoretical foundation and professional assistance for optimizing the shock impacts of these toxic substances on biological wastewater treatment systems, which will help to reduce their negative effects on treatment system efficiency.

A Review of the Role of Extracellular Polymeric Substances (EPS) in Wastewater Treatment Systems.

A review of the characterization and functions of extracellular polymeric substances (EPS) of microbial aggregates in biological wastewater treatment systems is presented in this paper. EPS represent the complex high-molecular-weight mixture of polymers excreted by microorganisms generated from cell lysis as well as adsorbed inorganic and organic matter from wastewater. EPS exhibit a three-dimensional, gel-like, highly hydrated matrix that facilitates microbial attachment, embedding, and immobilization. EPS play multiple roles in containments removal, and the main components of EPS crucially influence the properties of microbial aggregates, such as adsorption ability, stability, and formation capacity. Moreover, EPS are important to sludge bioflocculation, settleability, and dewatering properties and could be used as carbon and energy sources in wastewater treatment. However, due to the complex structure of EPS, related knowledge is incomplete, and further research is necessary to understand fully the precise roles in biological treatment processes.

Recovery Strategies for Heavy Metal-Inhibited Biological Nitrogen Removal from Wastewater Treatment Plants: A Review

Biological nutrient removal is an integral part of a wastewater treatment plant. However, the microorganism responsible for nutrient removal is susceptible to inhibition by external toxicants such as heavy metals which have the potential to completely inhibit biological nutrient removal. The inhibition is a result of the interaction between heavy metals with the cell membrane and the deoxyribonucleic acid (DNA) of the cell. Several attempts, such as the addition of pretreatment steps, have been made to prevent heavy metals from entering the biological wastewater systems. However, the unexpected introduction of heavy metals into wastewater treatment plants result in the inhibition of the biological wastewater treatment systems. This necessitates the recovery of the biological process. The biological processes may be recovered naturally. However, the natural recovery takes time; additionally, the biological process may not be fully recovered under natural conditions. Several methods have been explored to catalyze the recovery process of the biological wastewater treatment process. Four methods have been discussed in this paper. These include the application of physical methods, chelating agents, external field energy, and biological accelerants. These methods are compared for their ability to catalase the process, as well as their environmental friendliness. The application of bio-accelerant was shown to be superior to other recovery strategies that were also reviewed in this paper. Furthermore, the application of external field energy has also been shown to accelerate the recovery process. Although EDTA has been gaining popularity as an alternative recovery strategy, chelating agents have been shown to harm the metal acquisition of bacteria, thereby affecting other metabolic processes that require heavy metals in small amounts. It was then concluded that understanding the mechanism of inhibition by specific heavy metals, and understanding the key microorganism in the inhibited process, is key to developing an effective recovery strategy.