Tertiary Wastewater Treatment Processes Research Articles

Are algae a promising ecofriendly approach to micro/nanoplastic remediation?

How to reduce microplastic pollution in aquatic ecosystem has become the focus of the global attention. The re-removal of microplastics of wastewater treatment plant (WWTP) effluent is gradually being put on the agenda. Recently, algae have been used as an ecofriendly remediation strategy for microplastic removal. Microplastics in sewage can be removed by algae through interception, capture, and entanglement, and can also form heterogeneous aggregates with algae, thereby reducing their free suspensions. Algae can recover nitrogen and carbon from wastewater and can be made into biochar, biofertilizers, and biofuels. However, problematically, this technology has been in the laboratory research stage, and existing research results cannot provide effective basis for its application. Microplastic removal via algae is influenced by wastewater flow rate, microplastic types, and pollutants. Microplastics are only physically fixed by algae, and ensuring that microplastics do not re-enter the environment during resource and capacity recovery is also a key factor limiting the implementation of this technology. The topic of this paper is to discuss the performance of the current tertiary wastewater treatment process - algae process to remove microplastics. Algae can remove nitrogen and phosphorus pollutants in sewage and remove microplastics at the same time, which can realize energy recovery and reduce ecological risks of the effluent. Although algae combined tertiary sewage treatment is a green technology for microplastic removal, its application still needs to be explored. The key challenges that need to be addressed, from single laboratory conditions to complex conditions, from small-scale testing to large-scale simulations, lie ahead of the application of this friendly technology.

Tertiary Wastewater Treatment Processes Can Be a Double-Edged Sword for Water Quality Improvement in View of Mitigating Antimicrobial Resistance and Pathogenicity.

Despite the high removal efficiency for chemical pollutants by tertiary wastewater treatment processes (TWTPs), there is no definite conclusion in terms of microbial risk mitigation yet. This study utilized metagenomic approaches to reveal the alterations of antibiotic resistance genes (ARGs), virulence factor genes (VFGs), their co-occurrence, and potential hosts during multiple TWTPs. Results showed that the TWTPs reduced chemical pollutants in wastewater, but the denitrifying biofilter (DB) significantly increased the absolute abundances of selected antibiotic-resistant bacteria and ARGs, and simultaneously elevated the relative abundances of ARGs and VFGs through the enrichment of multidrug resistance and offensive genes, respectively. Moreover, the co-occurrence of ARGs and VFGs (e.g., bacA-tapW, mexF-adeG) was only identified after the DB treatment and all carried by Pseudomonas. Then, the ultraviolet and constructed wetland treatment showed good complementarity for microbial risk reduction through mitigating antibiotic resistance and pathogenicity. Network and binning analyses showed that the shift of key operational taxonomic units affiliating to Pseudomonas and Acinetobacter may contribute to the dynamic changes of ARGs and VFGs during the TWTPs. Overall, this study sheds new light on how the TWTPs affect the antibiotic resistome and VFG profiles and what TWTPs should be selected for microbial risk mitigation.

Evaluation of Membrane Fouling by Microplastic Particles in Tertiary Wastewater Treatment Processes

Microplastic (MP) pollution in aquatic environments poses substantial ecological, human, and economic threats. A common route of entry for MPs into the aquatic environment is through the effluent from wastewater treatment plants (WWTPs). Although membrane technologies as a tertiary treatment step have shown promise in mitigating the efflux of MPs, little is known about how MPs suspended in wastewater effluent affect membrane performance. One reason is that it is challenging to source MPs for filtration experiments which are representative of those found in WWTPs. As such, this study employed a milling and sieving process to create irregularly shaped polyethylene MPs approximately 10 μm in size which were then suspended in effluent wastewater (taken directly from a secondary clarifier tank). Membrane fouling caused by wastewater/MP interactions was investigated via constant pressure filtration experiments using commercial ultrafiltration and microfiltration membranes. It was found that even low concentrations of MPs in the wastewater increased the extent of membrane fouling. Furthermore, a backwashing process was found to significantly mitigate the effect of MP fouling on the membrane surfaces. The results from this study provide important insights into the governing factors for membrane fouling by MPs in water chemistries representative of WWTP effluents.

Wastewater substrate disinfection for cyanobacteria cultivation as tertiary treatment.

Cultivation of microalgae or/and cyanobacteria in nutrient-rich wastewaters offers an opportunity for enhancing sustainability of tertiary wastewater treatment processes via resources/energy recovery/production, mitigation of emitted GHGs and provision of added value products. However, maintaining a monoculture in wastewater-media constitutes a significant challenge to be addressed. In this regard, the present work assesses the efficiency of the low-cost wastewater substrate disinfection techniques of filtration, use of NaClO, H2O2 or Fe(VI), as a preliminary treatment stage upstream a cyanobacteria cultivation photobioreactor. The growth rate of cyanobacterium Synechococcus elongatus PCC 7942, and nitrate and phosphate removal rates, were experimentally assessed in cultivation setups with biologically treated dairy wastewater that had been subjected to a single or a synergetic couple of disinfection techniques. The results showed that filter thickness has a greater effect on disinfection efficiency than filter pore size. Furthermore, the disinfection efficiency of Fe(VI), which was produced on-site by electrosynthesis via a Fe0/Fe0 cell, was greater than that of NaClO and H2O2. Filtration at ≤ 1.2-μm pore size coupled with chemical disinfection led to unhindered Synechococcus elongatus PCC 7942 growth and efficient nitrate and phosphate removal rates, at dosages, in terms of Concentreation-Time (CT) product,of CT ≥ 270mgmin L-1 for NaClO and CT ≥ 157mgmin L-1 for Fe(VI). The coagulation action of Fe(III) species that result from Fe(VI) reduction and the oxidation action of Fe(VI) can assist in turbidity, organic compounds and phosphorous removal from wastewater media. Moreover, the residual iron species can assist in Synechococcus elongatus PCC 7942 harvesting and may enhance photosynthesis rate by increasing light transfer efficiency. Thus, a filtration configuration coupled with chemical disinfection, preferably using ferrates, downstream of sedimentation tank of a secondary biological wastewater treatment stage is proposed as a necessary, efficient and low-cost disinfection technique for full-scale scale implementation of cyanobacteria cultivation as tertiary wastewater processes.

Simultaneous removal of micropollutants, antibiotic resistant bacteria, and antibiotic resistance genes using graphitic carbon nitride under simulated solar irradiation

The prevalence of micropollutants (MPs) and antibiotic resistance in aquatic environments has raised increasing concern for public health and ecological security. Conventional wastewater treatment processes have limited efficiency to remove these emerging contaminants. Recently, photocatalytic processes have been proposed as a promising solution to achieve enhanced performance, but there are very few studies focusing on simultaneous removal of both chemical and biological contaminants. To test the technical feasibility of a “one-stop” photocatalytic process, we evaluated the photocatalytic performance of a urea-based graphitic carbon nitride (g-C3N4) for simultaneous removal of multiple MPs, as well as antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs). After a 10 min treatment under simulated solar irradiation, five MPs including sulfamethoxazole, diclofenac, mecoprop, benzotriazole, and carbamazepine (10 µg/L each) were effectively removed from spiked MilliQ water (88% of total removal efficiency) and real wastewater effluent (83% of total removal efficiency), respectively. In addition, 6.2-log reduction (complete inactivation) and 4.3-log reduction of ARB were observed after 60 min reaction in MilliQ water and real wastewater effluent, respectively. Moreover, ARB lost their self-repair function after the treatment. Lastly, atomic force microscopy images and qPCR analysis revealed that, not only the abundance of ARB but also extracellular ARGs (e-ARGs) decreased over the treatment peroid. Experiments trapping reactive species suggested that superoxide radicals (O2•-) and holes (h+) were the major active radicals contributing to contaminants degradation. The effective treatment performance for both chemical and biological contaminants, low manufacturing costs and ease of use make g-C3N4 a promising catalyst for application in the tertiary wastewater treatment processes.

Efficient photocatalytic destruction of recalcitrant micropollutants using graphitic carbon nitride under simulated sunlight irradiation

The ubiquity of micropollutants (MPs) in aquatic environments has attracted increasing concern for public health and ecological security. Compared to conventional biological treatment, photocatalytic processes show more efficiency in degrading MPs, but they require expensive materials and complicated synthesis processes. This study developed an economic photocatalytic process to degrade micropollutants. We synthesized urea-based graphitic carbon nitride (g-C3N4) by a facile one-step pyrolysis method and evaluated the photocatalytic efficiency of carbamazepine (CBZ). Under simulated solar irradiation, g-C3N4 could achieve 100% removal efficiency of 0.1 mg/L CBZ in spiked wastewater effluent within 15 min, and 86.5% removal efficiency in wastewater influent after 20 min of irradiation. The porous structure of g-C3N4 promoted effective charge separation and mass transport of CBZ near the catalyst surface, enabling a high kinetic rate (0.3662 min −1). Reactive oxygen species trapping experiments revealed that superoxide radicals (O2•-) and holes (h+) were the major active radicals. Electron paramagnetic resonance (EPR) further confirmed the presence of O2•-, • OH, 1O2 and holes. The pH, light intensity and initial CBZ concentration were found to have significant impacts on the removal efficiency of CBZ. Possible reaction intermediates were identified and the degradation pathway was proposed. Multiple MPs were selected to further demonstrate photocatalytic efficiency of g-C3N4. The facile synthesis, superior efficiency, and versatility of g-C3N4 make it a promising catalyst for application in tertiary wastewater treatment processes.

The novel SARS-CoV-2 pandemic: Possible environmental transmission, detection, persistence and fate during wastewater and water treatment

The contagious SARS-CoV-2 virus, responsible for COVID-19 disease, has infected over 27 million people across the globe within a few months. While literature on SARS-CoV-2 indicates that its transmission may occur predominantly via aerosolization of virus-laden droplets, the possibility of alternate routes of transmission and/or reinfection via the environment requires considerable scientific attention. This review aims to collate information on possible transmission routes of this virus, to ascertain its fate in the environment. Concomitant with the presence of SARS-CoV-2 viral RNA in faeces and saliva of infected patients, studies also indicated its occurrence in raw wastewater, primary sludge and river water. Therefore sewerage system could be a possible route of virus outbreak, a possible tool to assess viral community spread and future surveillance technique. Hence, this review looked into detection, occurrence and fate of SARS-CoV-2 during primary, secondary, and tertiary wastewater and water treatment processes based on published literature on SARS-CoV and other enveloped viruses. The review also highlights the need for focused research on occurrence and fate of SARS-CoV-2 in various environmental matrices. Utilization of this information in environmental transmission models developed for other enveloped and enteric viruses can facilitate risk assessment studies. Preliminary research efforts with SARS-CoV-2 and established scientific reports on other coronaviruses indicate that the threat of virus transmission from the aquatic environment may be currently non-existent. However, the presence of viral RNA in wastewater provides an early warning that highlights the need for effective sewage treatment to prevent a future outbreak of SARS-CoV-2.

Environmental impacts of an advanced oxidation process as tertiary treatment in a wastewater treatment plant

Due to global water scarcity, the use of reclaimed wastewater for crop irrigation is required; however, if the wastewater treatment is inadequate, it can be a source of environmental pollution. In order to improve wastewater reclamation, advanced oxidation processes (AOPs) have been tested. At full scale, ozonation is one such process that effectively removes micropollutants, despite its high-energy consumption. At pilot scale, other technologies such as the solar photo-Fenton process are being developed. This process is under consideration as a sustainable technology because it uses sunlight as a source of radiation. However, there is little information available on its environmental performance. In this work, we perform a comparative analysis between the ozonation and the photo-Fenton process as tertiary wastewater treatment processes used to reclaim wastewater for agricultural irrigation. We apply the Life Cycle Assessment (LCA) methodology for quantifying environmental impacts with ReCiPe and USEtox as life cycle impact assessment (LCIA) methods. The results show that both tertiary treatment options reduce water stress locally. Ozonation has a better overall environmental performance compared to the photo-Fenton process because the environmental impact of the required ozone is smaller than of the reactants involved in the solar photo-Fenton. Moreover, the first can be operated both day and night, and therefore needs no additional storage for collecting the nightly secondary effluent, and thus has lower infrastructure related impacts. Additionally, when the solar photo-Fenton process operates at an acidic pH, there are environmental drawbacks related to the pH adjustment, which consumes a large amount of acid thus liberating CO2. Finally, the environmental impacts associated with the discharge of micropollutants to soil through the use of reclaimed water are very small compared to the other impacts generated by the treatment. However, due to the current LCIA method limitations of micropollutant impact assessment, these are subject to major uncertainty.

Phenolic compounds removal by grasses and soil bacteria after land application of treated palm oil mill effluent: A pot study

Land application of treated palm oil mill effluent (TPOME) could be used as an alternative tertiary wastewater treatment process. However, phenolic compounds in TPOME might be leached to the environment. This study investigated the ability of grasses on reducing phenolic compounds in the leachate after TPOME application. Several pasture grasses in soil pots were compared after irrigating with TPOME from stabilization ponds, which contained 360–630 mg/L phenolic compounds. The number of soil bacteria in planted pots increased over time with the average of 108 CFU/g for mature grasses, while only 104–106 CFU/g were found in the unplanted control pots. The leachates from TPOME irrigated grass pots contained lower amounts of phenolic compounds and had lower phytotoxicity than that of control pots. The phenol removal efficiency of grass pots was ranged 67–93% and depended on grass cultivars, initial concentration of phenolic compounds and frequency of irrigations. When compared to water irrigation, TPOME led to an increased phenolic compounds accumulation in grass tissues and decreased biomass of Brachiaria hybrid and Brachiaria humidicola but not Panicum maximum. Consequently, the application of TPOME could be conducted on grassland and the grass species should be selected based on the utilization of grass biomass afterward. Keywords: Land application, Palm oil mill effluent, Phenolic compounds, Rhizoremediation, Wastewater treatment

The Effect of Primary, Secondary, and Tertiary Wastewater Treatment Processes on Antibiotic Resistance Gene (ARG) Concentrations in Solid and Dissolved Wastewater Fractions

Wastewater treatment plants (WWTPs) have been identified as potential sources of antibiotic resistance genes (ARGs) but the effects of tertiary wastewater treatment processes on ARGs have not been well characterized. Therefore, the objective of this study was to determine the fate of ARGs throughout a tertiary-stage WWTP. Two ARGs, sul1 and bla, were quantified via quantitative polymerase chain reaction (qPCR) in solids and dissolved fractions of raw sewage, activated sludge, secondary effluent and tertiary effluent from a full-scale WWTP. Tertiary media filtration and chlorine disinfection were studied further with the use of a pilot-scale media filter. Results showed that both genes were reduced at each successive stage of treatment in the dissolved fraction. The solids-associated ARGs increased during activated sludge stage and were reduced in each subsequent stage. Overall reductions were approximately four log10 with the tertiary media filtration and disinfection providing the largest decrease. The majority of ARGs were solids-associated except for in the tertiary effluent. There was no evidence for positive selection of ARGs during treatment. The removal of ARGs by chlorine was improved by filtration compared to unfiltered, chlorinated secondary effluent. This study demonstrates that tertiary-stage WWTPs with disinfection can provide superior removal of ARGs compared to secondary treatment alone.

Porous materials for the sorption of emerging organic pollutants from aqueous systems: The case for conjugated microporous polymers

Emerging organic pollutants (EOPs) pose a challenge to water treatment facilities and are a potential hazard to the environment and human health. Potential ways of removing these pollutants in tertiary wastewater treatment processes to make it potable include the use of porous materials like biochar, zeolites, metal organic frameworks (MOFs), covalent organic frameworks (COFs), polymers of intrinsic microporosity (PIMs), zirconium based porous materials and, more recently, conjugated microporous polymers (CMPs). CMPs have attracted research attention owing to their porosity and π-conjugation which can easily be engineered for a wide range of applications. The synthesis of CMPs is relatively easily done through established pathways that include the Suzuki coupling, Sonogashira-Hagihara cross-coupling, Friedel-Crafts reactions, oxidative coupling, Ullmann reaction and the Yamamoto coupling. Post-synthetic functionalisation approaches have been used to obtain CMPs which have specific motifs suited for particular applications. Despite their potential, use of CMPs in removing EOPs from water has not received adequate research attention, and is therefore an area that needs research. This short communication highlights the challenges posed by EOPs, presents some of the possible porous materials that can be used for their removal, and proposes CMPs as suitable potential adsorbents. Basing on recent literature covering the period 2003–2016, the synthetic methods, properties and applications of these materials have been presented.

Electrochemical disinfection and removal of ammonia nitrogen for the reclamation of wastewater treatment plant effluent.

Residual ammonia and pathogenic microorganisms restrict the reclamation and reuse of wastewater treatment plant (WWTP) effluent. An electrochemical system was developed for the simultaneous removal of ammonia and disinfection of actual WWTP effluent. The performance of the electrochemical process on synthetic wastewater at different chloride ion concentrations was also investigated. Results demonstrated that the optimal chloride concentration for ammonia and Escherichia coli (E. coli) removal was 250mg/L. Successful disinfection of E. coli in actual effluent was achieved at 0.072Ah/L, but the inverse S-type inactivation curve indicated that there was a competitive consumption of strong oxidants and chloramines working as another disinfectant. A higher electric charge (0.58Ah/L) was required to simultaneously reduce E. coli and ammonia to levels that meet the reclamation requirements for WWTP effluent. At this electric charge, no trihalomethane, chlorate, or perchlorate in the system was observed, indicating the biological safety of this process. These results demonstrate the potential of this electrochemical process as a tertiary wastewater treatment process for WWTP effluent reclamation purposes.

Survival of Helicobacter pylori in the wastewater treatment process and the receiving river in Michigan, USA.

Contaminated water may play a key role in the transmission of Helicobacter pylori, resulting in gastrointestinal diseases in humans. The wastewater treatment process is an important barrier to control the transmission of H. pylori. However, the presence and viability of H. pylori in the treatment process is not well known. In this paper, the real colony morphology of H. pylori was confirmed by two types of culture media. The survival of H. pylori through the tertiary wastewater treatment process, especially UV disinfection, and in the receiving Huron River in Ann Arbor, Michigan, was investigated by plates cultivation, regular polymerase chain reaction (PCR) assays and quantitative real-time PCR from DNA. The results demonstrated that H. pylori was not only present, but also viable in all processed wastewater samples in the Ann Arbor wastewater treatment plant (WWTP). H. pylori can be found in a higher concentration in the receiving Huron River. There are many kinds of antibiotic- and UV-resistant bacteria, including H. pylori, in the final effluent of Ann Arbor WWTP.

Effects of plant biomass on bacterial community structure in constructed wetlands used for tertiary wastewater treatment

Constructed wetlands (CWs) have been used successfully to treat municipal wastewater. However, few studies have focused on the microbial community in CWs used for tertiary wastewater treatment. In this study, 454 high-throughput pyrosequencing was applied to analyze the bacterial community in unplanted, planted, and litter loaded CWs. Results showed that both plants and litter increased the diversity and abundance of the microbial community in CWs. The effects of plant biomass on the bacterial community at the phylum level were not pronounced, but the compositions were significantly affected at the class and genus levels. Specific comparison down to the genus level revealed that the relative abundances of nitrifier, denitrifier and sulfate-reducing bacteria were positively correlated with the removal efficiencies of ammonia, nitrate and sulfate observed. Highly functional organization (>70%) of the bacterial communities indicates that only a small group of species played a dominant role in CWs. The presence of plants and litter significantly affected the bacterial composition via alteration of carbon content (%) and pH values in the gravel matrix. The observation in this study provides useful information about the effects of plant biomass on the bacterial community structure, which plays an important role in the tertiary wastewater treatment process in CWs.

A study on the effects of ozone dosage on dissolved-ozone flotation (DOF) process performance

Dissolved-ozone flotation (DOF) is a tertiary wastewater treatment process, which combines ozonation and flotation. In this paper, a pilot-scale DOF system fed by secondary effluent from a wastewater treatment plant (WWTP) in China was used to study the effect of ozone dosage on the DOF process performance. The results show that an ozone dosage could affect the DOF performance to a large extent in terms of color and organic matter removal as well as disinfection performance. The optimal color and organic matter removal was achieved at an ozone dosage of 0.8 mg/l. For disinfection, significant improvement in performance could be achieved only when the organic matter removal was optimal. The optimal ozone dosage of at least 1.6 mg/l was put forward, in this case, in order to achieve the optimal color, turbidity, organic matter and disinfection performance.

Laccases to take on the challenge of emerging organic contaminants in wastewater.

The removal of emerging organic contaminants from municipal wastewater poses a major challenge unsatisfactorily addressed by present wastewater treatment processes. Enzyme-catalyzed transformation of emerging organic contaminants (EOC) has been proposed as a possible solution to this major environmental issue more than a decade ago. Especially, laccases gained interest in this context in recent years due to their broad substrate range and since they only need molecular oxygen as a cosubstrate. In order to ensure the stability of the enzymes and allow their retention and reuse, either immobilization or insolubilization of the biocatalysts seems to be the prerequisite for continuous wastewater treatment applications. The present review summarizes the research conducted on EOC transformation with laccases and presents an overview of the possible immobilization techniques. The goal is to assess the state of the art and identify the next necessary steps that have to be undertaken in order to implement laccases as a tertiary wastewater treatment process in sewage treatment plants.

Hydrodynamic regime considerations for the cultivation of periphytic biofilms in two tertiary wastewater treatment systems

As the demand for biofuel products continues to rise along with the need for tertiary wastewater treatment processes to facilitate the removal of phosphorus, increasing importance is placed on the design of cultivation systems for the production of algal biomass. In addition to traditional open ponds and photobioreactors, attached algal growth systems can provide high rates of biomass production while simultaneously removing nutrients from wastewater effluent. The potential economic viability of these attached growth systems is dependent on the optimization of bed flow characteristics, inflow water quality parameters, and hydrodynamic regimes in order to maximize biomass productivity. This study monitored the productivity and nutrient removal rates of a pilot-scale attached growth system (AGS1) used to remove phosphorus from wastewater effluent at a municipal wastewater treatment plant in Fayetteville, Arkansas. These results were compared with the results from a similar system in the same watershed that was monitored in a previous study (AGS2). The performance of AGS2 was documented in a companion article in Ecological Engineering. In spite of the similarities between the systems’ locations and influent characteristics, the productivities of the two systems were very different. The rates of biomass production in AGS1 and AGS2 were 4.4±4.8 and 26.7±16.0gdry weightm−2d−1, respectively. Potential reasons for the dramatic differences in performance between the two systems are explored in this article.

The effect of UV-C radiation (254 nm) on candidate microbial source tracking phages infecting a human-specific strain of Bacteroides fragilis (GB-124)

The enumeration of phages infecting host-specific strains of Bacteroides has been widely recognised as an effective and low-cost method of microbial source tracking (MST). A recently described human-specific Bacteroides host strain (GB-124) has been shown to detect bacteriophages exclusively in human-impacted waters and is emerging as a useful MST tool. However, a better understanding of the morphology and ecological behaviour of the phages, especially in wastewater disinfection processes, is now required in order to validate their role as MST markers. Bacteriophages infecting Bacteroides fragilis GB-124 (n = 21) were isolated from wastewater effluent and irradiated using laboratory-based UV-C (254 nm) collimated beam experiments. Bacteriophages were found to be both a morphologically and ecologically homogeneous group, with all specimens showing highly similar first order log-linear inactivation profiles (mean fluence required to inactivate phages by 4-log(10) was 36 mJ/cm(2)). These findings present the first evidence that phages infecting GB-124 are inactivated by the levels of UV-C radiation routinely delivered during tertiary wastewater treatment processes. More importantly, comparison with previously published inactivation data suggests that their response to UV-C radiation makes GB-124 phages more suitable surrogates for selected enteric viruses in UV disinfection processes than traditional faecal indicator bacteria or human-specific molecular markers.

Evaluation of sewage sludge production and utilization in Greece in the frame of integrated energy recovery

The objectives of this work were to provide an overview of municipal activated sludge units in Greece, to determine the sludge annual production rates and to examine potential for energy utilization of dewatered sludge. 37 wastewater treatment plants, serving a population equivalent of 1.6 million, located throughout Greece, were investigated during this study, in order to determine the sludge production rate after secondary and tertiary wastewater treatment processes. The average sludge production amount was estimated at 0.04 kg dry matter per capita per day, corresponding to an average wastewater production rate of 246 L per capita and day. Tertiary processes resulted to higher amounts of sludge production; nevertheless, such processes are often required aiming to the reclamation of secondary effluents with a high reuse and acceptability potential. Considering the disposal cost of produced sludge, energy utilization could be a promising alternative method for efficient sludge management. Utilization of the energy content of the sludge was examined by using three options, consisting in anaerobic digestion of dewatered sludge, incineration, and anaerobic digestion followed by residue incineration; it was found that excess energy production reached to high values in the case of combined anaerobic digestion and incineration, while single anaerobic digestion resulted to the lowest power production rates.

Modeling of Headloss Development in Biological Aerated Filter (<i>BAF</i>) —Ⅰ. Equations Development

Biological Aerated Filter (BAF) has been global applied in secondary and tertiary wastewater treatment process in the past decades. As the increasing application of BAF, it was required to get deeper understanding of the operational discipline, parameter optimization and structural characteristics of BAF to improve the treatment efficiency and to operate stability constantly. In this paper, a physical filtration equation of clean filter bed was established firstly based on an average porosity ratio equation and Kozeny-Carman filtration equation. And then the influence of biological oxidation and biofilm development were introduced, of which the Eckenfelder mode and oxygen transfer were considered, to induce a hybrid physical- biologically equation to describe the headloss development in the BAF.