Aerobic Wastewater Treatment Research Articles

Scaling up Microbial Fuel Cells for Treating Swine Wastewater

Conventional aerobic treatment of swine wastewater, which generally contains 4500–8200 mg L−1 of organic matter, is energy-consuming. The aim of this study was to assess the application of scaled-up microbial fuel cells (MFCs) with different capacities (i.e., 1.5 L, 12 L, and 100 L) for removing organic matter from swine wastewater. The MFCs were single-chambered, consisting of an anode of microbially reduced graphene oxide (rGO) and an air-cathode of platinum-coated carbon cloth. The MFCs were polarized via an external resistance of 3–10 Ω for 40 days for the 1.5 L-MFC and 120 days for the 12L- and 100 L-MFC. The MFCs were operated in continuous flow mode (hydraulic retention time: 3–5 days). The 100 L-MFC achieved an average chemical oxygen demand (COD) removal efficiency of 52%, which corresponded to a COD removal rate of 530 mg L−1 d−1. Moreover, the 100 L-MFC showed an average and maximum electricity generation of 0.6 and 2.2 Wh m−3, respectively. Our findings suggest that MFCs can effectively be used for swine wastewater treatment coupled with the simultaneous generation of electricity.

Disentanglement of the chemical, physical, and biological processes aids the development of quantitative structure-biodegradation relationships for aerobic wastewater treatment

Attenuation of organic compounds in sewage treatment plants (STPs) is affected by a complex interplay between chemical (e.g. ionization, hydrolysis), physical (e.g. sorption, volatilization), and biological (e.g. biodegradation, microbial acclimation) processes. These effects should be accounted for individually, in order to develop predictive cheminformatics tools for STPs. Using measured data from 70 STPs in the Netherlands for 69 chemicals (pharmaceuticals, herbicides, etc.), we highlighted the influences of 1) chemical ionization, 2) sorption to sludge, and 3) acclimation of the microbial consortia on the primary removal of chemicals. We used semi-empirical corrections for each of these influences to deduce biodegradation rate constants upon which quantitative structure-biodegradation relationships (QSBRs) were developed. As shown by a global QSBR, biodegradation in STPs generally relates to structural complexity, size, energetics, and charge distribution. Statistics of the global QSBR were reasonable, being R2training=0.69 (training set of 51 compounds) and R2validation=0.50 (validation set of 18 compounds). Class-specific QSBRs utilized electronic properties potentially relating to rate-limiting enzymatic steps. For class-specific QSBRs, values of R2 of in between 0.7 and 0.8 were obtained. With caution, environmental risk assessment methodologies may apply these models to estimate biodegradation rates for ‘data-poor’ compounds. The approach also highlights ‘meta data’ on STP operational parameters needed to develop QSBRs of better predictability in the future.

Self-build packed-bed bioreactor for rapid and effective BOD estimation.

This work demonstrated a simple, low-cost, rapid, and effective biochemical oxygen demand (BOD) estimation system based on a packed-bed bioreactor that can be easily self-built on-site at a particular wastewater treatment plant for continuous monitoring of the influent and effluent. The use of natural microbial consortium that were collected from the target wastewater and immobilized on a cheap porous carrier simply by adhesion resulted in an acceptable accuracy of over 95%. The newly developed semi-continuous operating mode with peak-type signals was shown to be able to continuously estimate BOD at a high flow rate to overcome the flow dependence of the oxygen electrode, limit clogging issues, enhance the response time, and lower the limit of detection. The resulting packed-bed bioreactors could work continuously for 22h with a coefficient of variance (CoV) of only 1.8% or for 13h a day for several days with a maximum CoV of 1.4% and their response was observed to be stable over 80 consecutive measurements. They exhibited stable responses at a wide pH range of 6.5-8.5, which is also the recommended range for aerobic wastewater treatment, emphasizing the greater ease of use of natural microorganisms for BOD estimation.

Characteristics of an aerobic denitrifier isolated from unconfined aquifer

An aerobic denitrifier strain named X11 was isolated from the shallow unconfined aquifer samples in Suzhou city, China. According to the physiological biochemical identification and the 16S rDNA gene analysis, the strain X11 was generally identified as Pseudomonadales Pseudomonadaceae. Single factor experiments were used to investigate the influence of temperature, pH and carbon sources on its growth and denitrification characteristics. The results showed that under aerobic conditions the total nitrogen loss and nitrate reduction efficiency within 60 hours were up to 70.3% and 95.1%, respectively, with initial nitrate concentration of 276.25 mg/L. The nitrate removal rates reached 18.24 mg/L·h within 12 hours. It was found that strain X11 can convert nitrate into nitrogen gas without obvious accumulation of nitrite under aerobic conditions. The pH increased and ORP decreased by activated denitrifier in liquid medium. the optimum conditions were obtained as follows; temperature value of 30° C, pH value of 7. The results indicate that the isolated aerobic denitrifier XK11 has high nitrogen removal efficiency, it may be a good candidate for in-situ bioremediation of nitrogen-contaminated shallow groundwater or aerobic wastewater treatment.

Modeling and research of the biological water treatment process considering the temperature regime

Household waste water contains mineral and organic pollution, while industrial varies both in composition and concentration, depending of the origin. Whatever type, all waste water required to be cleaned as it contains pollutants which far exceed the permissible concentration limits. Despite the large number of investigations of the corresponding processes, the actual task is to study the interaction of active sludge with pollution under the influence of external factors such as variable temperature, etc. Another important task is the prediction of process parameters waste water treatment based on the information with incomplete data at the design stage of the purification system. The automation of processes occurring in the reactor, in particular the use of bacteria with the optimal age, the creation of conditions for the maximum absorption capacity of active sludge, minimization of economic costs are integral components of modern systems.The mathematical model of aerobic waste water treatment is developed, which describes the processes occurring in the treatment plant taking into account the mutual influences of the characteristics of the process on the characteristics of the environment. The influence of external factors for the temperature calculation on the basis of the equation of thermal balance and the laws of thermodynamics is taken into account. The solution of the corresponding model problem using the m-function pdepe of the Matlab software is found. The influence of temperature of aqueous environment, concentration of oxygen on the absorbing capacity of active sludge is investigated. The dependence of bacterial activity from water temperature is shown.

Impact of the filamentous fungi overgrowth on the aerobic granular sludge process

The aerobic granular sludge wastewater treatment technology has numerous advantages as compared to the conventional flocculent sludge technologies. However, the filamentous fungi overgrowth (FFO) is a major operational problem that is hindering its widespread application. This study evaluated the behaviour and mechanisms of the FFO, and its impact on granulation, treatment performance and microbial community structure. The overgrown filamentous organisms were developed in an aerobic granular sludge reactor operated for 274 days. The filamentous organisms were identified to be yeast-like fungi belonging to the moulds Geotrichum of the phylum Ascomycota. The removal of carbon and nitrogen were slightly affected, while phosphorus removal was largely impacted. The FFO development was found to disrupt the structural integrity of granules, cause their disintegration and washout, and lead to a microbial community shift towards a structure lacking bacteria genus that are essential for efficient granulation. Limitations of the currently used routine measurements were discussed.

Microbial fuel cells (MFCs) for bioelectrochemical treatment of different wastewater streams

Wastewaters generated from several industrial sources containing organic substrates present a vital basis for harnessing bioenergy. Aerobic wastewater treatment methods, for instance, activated sludge process and trickling filter are unsustainable due to constant energy requirements for aeration, and sludge management. Currently, Microbial Fuel Cell (MFC) technology presents an appropriate alternative for energy positive wastewater treatment and permits synchronized wastewater treatment, bioelectricity production, and resource recovery via bioelectrochemical remediation mediated by electroactive microbes. The added advantage of using MFC technology for effluent treatment is that several bio-based processes including removal of biochemical and chemical oxygen demand, nitrification, denitrification, sulfate removal and removal of heavy metals can be carried out in the same bioreactor. Thus, MFCs can both substitute and complement the conventional energy-intensive technologies for efficient removal as well as the recovery of sulfate, nitrogen, and phosphate without any tertiary treatment. Thus, the present review covers the recent advances in the utilization of microbial fuel cell technology for the removal of organic as well as recalcitrant pollutants from a wide range of industrial and domestic effluents with the simultaneous production of low-cost energy. Further this review discusses the hybrid systems developed in integration with conventional treatment systems to make the process energy neutral and thus pave a way to scale-up the MFCs for sustainable wastewater treatment. Moreover, some critical challenges related to the field applications of microbial fuel cell technology dealing with a wide range of effluents, have also been analyzed and presented.

Sulfate reducing bacteria-based wastewater treatment system integrated with sulfide fuel cell for simultaneous wastewater treatment and electricity generation

This study aimed to design a sulfate-reducing bacteria (SRB)-based wastewater treatment system (SWTS) integrated with a sulfide fuel cell (SFC) as an alternative to the energy-intensive aerobic wastewater treatment process. The result showed that the COD/sulfate ratio and hydraulic retention time (HRT) were two important parameters in a SWTS. The highest COD and sulfate removal efficiency rates were at a HRT of 4 h at a COD/sulfate ratio of 0.67, reaching 83 ± 0.2% and 84 ± 0.4% with sulfate removal rates of 4.087 ± 32 mg SO42−/d, respectively. A microbial analysis revealed that the dominance of nine OTUs belonging to SRB closely affected the high sulfate removal efficiency in the SWTS. At the HRT of 8 h, voltage of 0.02 V and a power density level of 130 mW/m2 were obtained with sulfide removal efficiency of 99 ± 0.5%. These results overall demonstrate that SRB can serve as a green and effective route for wastewater treatment.

China's Urban Methane Emissions From Municipal Wastewater Treatment Plant

AbstractThe increased number and capacity of municipal wastewater treatment plants (WWTPs) in China has driven the emission of methane (CH4). Few studies have focused on quantification of CH4 emissions from municipal WWTPs of different cities and analysis of socioeconomic factors influencing the quantity of emissions. Here we estimated CH4 emissions from WWTPs in China for 229 prefectural‐level cities, based on data from 2,019 working municipal WWTPs. The results show the total CH4 emissions to be 1,169.8 thousand tons (29.2 MtCO2e) in 2014, which is over three times that of the municipal WWTPs in the United States in 2016. Large cities along the east coast regions had larger CH4 emissions in absolute and per capita terms. Correlation analysis shows that cities with higher gross domestic product, household food consumption expenditure, or household consumption expenditure produced more degradable organics in wastewater, thus more CH4 emissions. Measures to control the sources of degradable organics and regulate WWTP processes with less emission factor are key to mitigate CH4 emissions. In addition to aerobic or anaerobic wastewater treatment systems, factors such as wastewater temperature, length of sewer, and the addition of nitrate that influencing emission factor are suggested to be involved in CH4 emission modeling.

Energy efficient COD and N-removal from high-strength wastewater by a passively aerated GAO dominated biofilm

Conventional aerobic treatment of high-strength wastewater is not economical due to excessively high energy requirement for compressed air supply. The use of passive aeration avoids the use of compressed air and enables energy efficient oxygen supply directly from the air. This study evaluates a passively aerated simultaneous nitrification and denitrification performing biofilm to treat concentrated wastewater. The biofilm reactor was operated > 5-months under alternating anaerobic/aerobic conditions. For 4-times concentrated wastewater, > 80% COD (2307 mg L−1 h−1) and > 60% N (60 mg L−1 h−1) was removed at a hydraulic retention time (HRT) of 7 h. A double application in the same reactor enabled > 95% COD and 85% N-removal, at an overall HRT of 14 h which is substantially shorter than what traditional activated sludge-based systems would require for the treatment of such concentrated feeds. Microbial community analysis showed Candidatus competibacter (27%) and nitrifying bacteria (Nitrosomonas, and Nitrospira) as key microbes involved in COD and N-removal, respectively.

Why Novel Sanitary Systems are Hardly Introduced?

Innovations are required in urban infrastructures due to the pressing needs for mitigating climate change and prevent resource depletion. In order to address the slow pace of innovation in urban systems, this paper analyses factors involved in attempts to introduce novel sanitary systems. Today new requirements are important: sanitary systems should have an optimal energy/climate performance, with recovery of resources, and with fewer emissions. Anaerobic digestion has been suggested as an alternative to current aerobic waste water treatment processes. This paper presents an overview of attempts to introduce novel anaerobic sanitation systems for domestic sanitation. The paper identifies main factors that contributed to a premature termination of such attempts. Especially smaller scale anaerobic sanitation systems will probably not be able to compete economically with traditional sewage treatment. However, anaerobic treatment has various advantages for mitigating climate change, removing persistent chemicals, and for the transition to a circular economy. The paper concludes that loss avoidance, both in the sewage system and in the waste water treatment plants, should play a key role in determining experiments that could lead to a transition in sanitation.

Performance and Applications of Semifluidized Bioreactors – A Review

AbstractThis paper reviews the design features and performance characteristics of semifluidized bed bioreactors. Both biofilm reactors and immobilized enzyme bioreactors have been analysed. Also, both two phase (liquid – solid) and three phase (gas – liquid – solid) operations are considered. Apart from the hydrodynamic parameters (semifluidization velocity, bed expansion ratio, height of packed section formed, fractional fluid holdups in both fluidized and packed sections), all other operating/system parameters affecting reactor performance such as axial dispersion, intrinsic kinetics of bioconversion (mostly nonlinear), the effectiveness factor and Thiele – type modulus have also been surveyed. The specific advantages and attractive features of these bioreactors have been highlighted based on data from successful case studies such as bioplastic synthesis, biodiesel manufacture, Xanthan gum production and aerobic waste water treatment with and without LPO (Liquid Phase Oxygen) utilization.

DEGRADATION RATE OF LIMED SEWAGE SLUDGE IN AN AGRICULTURAL SOIL

Little is known about the degradation kinetics of sewage sludge, sanitized with Ca(OH)2, in soil. Thus, this work aimed to monitor the degradation of limed sludge, under field conditions, when applied on soil surface or incorporated into the soil. The limed sludge was applied in dystrophic Inceptisol at a dose of 500 kg ha-1 yr-1 of total nitrogen. The mineralization process in the soil was monitored for 131 days. Samples of organic material were collected for analysis of total and easily oxidizable organic carbon; total, ammonium, nitric and organic nitrogen; volatile solids; and water contents. The undigested secondary sewage sludge generated in wastewater aerobic treatment mineralizes faster when limed and incorporated, compared to being arranged on soil surface. The estimated annual mineralization fraction of the limed sludge was 100% and greater than 95%, when incorporated or arranged on soil surface, respectively. Such values are higher than those established in the Brazilian environmental legislation for undigested sewage sludge disposal on soil.

A full-scale hybrid vertical anaerobic and aerobic biofilm wastewater treatment system: case study

Abstract The first full-scale Hybrid Vertical Anaerobic Aerobic Biofilm (HyVAB) reactor has been set up for treating wastewater from a vegetable processing industry in Grimstad, Norway. The novel HyVAB reactor integrates a bottom expanded granular sludge bed with a top aerobic biofilm stage, resulting in a small footprint and high treatment efficiency. The full scale holistic treatment plant consists of a pretreatment system of a sand trap and an equalization tank, a HyVAB reactor and an effluent sludge settlement tank. The HyVAB system has been operated continuously for 219 days with flow and chemical oxygen demand (COD) fluctuations corresponding to different product seasons. The reactor hydraulic retention time ranges from 32 to 10 hours, with the anaerobic organic loading rate (OLR) reaching a maximum 16 kg-COD/m3·d. The HyVAB removed on average of 90% of the total feed COD, at an operational temperature of 25 °C. Sludge production was low at 0.11 kg-volatile suspended solids/kg-COD removed. Odorless effluent from HyVAB can be discharged directly to a local municipal wastewater treatment plant without sludge handling. Over 82% of feed COD was converted to methane, leaving high methane content (84 ± 2%) biogas out of the reactor. Energy consumption of HyVAB was 0.5 kwh/ton wastewater. The cost of wastewater treatment is 1.5 NOK/kg COD removed (based on rates in Norway).

Effect of aeration on residence time in biological wastewater treatment

Aerobic wastewater treatment requires extensive aeration, which primary function is to provide oxygen to the biomass responsible for degradation of wastewater constituents. Besides the effective oxygen transfer efficiency aeration is responsible for fluid flow created by bubbles. In this research bubbles were released from plate diffusers and the impact on mixing were analyzed. Various aeration flow rates and initial bubble sizes were calculated. Residence time distributions in each scenario were compared applying numerical tracer study. Outcome of the calculations is that the aeration reduces the theoretical residence time significantly and therefore the traditional sizing methods needs to be revisit in wastewater treatment.

The influence of solid-liquid coefficient in the fate of pharmaceuticals and personal care products in aerobic wastewater treatment.

Wastewater treatment plants (WWTPs) are considered to be a source of environmental contamination by micropollutants, especially from pharmaceuticals and personal care products (PCPs). The pathway of those compounds during sewage treatment has been investigated, but data from real-scale WWTPs is still missing (for example, the values of the solid-liquid coefficient (Kd) during treatment). This paper uses the Kd values for some pharmaceuticals and PCPs (fenofibrate, gemfibrozil, propranolol, metoprolol, salicylic acid, acetylsalicylic acid, ibuprofen, diclofenac, naproxen, fenoprofen, caffeine, triclosan, methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben) to describe the micropollutants' behavior in the treatment process. In order to attain this data, an aerobic wastewater treatment plant located in Brazil was studied. Six samplings were carried out and a mass balance was performed, associating the concentrations of the micropollutants in the liquid phase with the solid phase (sludge and suspended solids). Of all the compounds analyzed, caffeine was the most biodegradable pollutant, as almost 98% of its mass was biodegraded. In contrast, triclosan had the highest load in sludge (median of 163.0mgday-1) and adsorbed in SS (median of 0.593mgday-1) at the output. Summing up, each micropollutant had a specific way to be removed during wastewater treatment.

Methane correction factors for estimating emissions from aerobic wastewater treatment facilities based on field data in Mexico and on literature review

Wastewater treatment (WWT) may be an important source of methane (CH4), a greenhouse gas with significant global warming potential. Sources of CH4 emissions from WWT facilities can be found in the water and in the sludge process lines. Among the methodologies for estimating CH4 emissions inventories from WWT, the more adopted are the guidelines of the Intergovernmental Panel on Climate Change (IPCC), which recommends default emission factors (Tier 1) depending on WWT systems. Recent published results show that well managed treatment facilities may emit CH4, due to dissolved CH4 in the influent wastewater; in addition, biological nutrient removal also will produce this gas in the anaerobic (or anoxic) steps. However, none of these elements is considered in the current IPCC guidelines. The aim of this work is to propose modified (and new) methane correction factors (MCF) regarding the current Tier 1 IPCC guidelines for CH4 emissions from aerobic treatment systems, with and without anaerobic sludge digesters, focusing on intertropical countries. The modifications are supported on in situ assessment of fugitive CH4 emissions in two facilities in Mexico and on relevant literature data. In the case of well-managed centralized aerobic treatment plant, a MCF of 0.06 (instead of the current 0.0) is proposed, considering that the assumption of a CH4-neutral treatment facility, as established in the IPCC methodology, is not supported. Similarly, a MCF of 0.08 is proposed for biological nutrient removal processes, being a new entry in the guidelines. Finally, a one-step straightforward calculation is proposed for centralized aerobic treatment plants with anaerobic digesters that avoids confusion when selecting the appropriate default MCF based on the Tier 1 IPCC guidelines.

Elimination of hydrogen sulfide from biogas by a two-stage trickling filter system using effluent from anaerobic–aerobic wastewater treatment

This study presents a two-stage desulfurization system based on two trickling filters (TFs): a first-stage closed-type TF (1st TF) and an open-type second-stage TF without aeration (2 nd TF). The effluent from an anaerobic–aerobic wastewater treatment system served as the water source, and coconut chips were used as the packing media for both the TFs. The concentration of hydrogen sulfide in the biogas ranged from 80 to 2300 ppm (v/v) with an average concentration of 737 ppm. The 1st TF eliminated more than 99% of the hydrogen sulfide at a loading rate of 5.24 gS–H2S m−3 h−1. Subsequently, 50.0% of the eliminated hydrogen sulfide was oxidized to sulfate in the 2 nd TF without aeration. The two-stage TF system additionally eliminated 53.1% of ammonia from among which 52.6% was detected as nitrate in the effluent of the 2 nd TF. Additionally, 9.2% of the total nitrogen was eliminated by the 2 nd TF. These results indicate that some of the dissolved sulfide was oxidized to elemental sulfur and/or thiosulfate; further, and sulfur-based autotrophic denitrification was observed to occur in the 2 nd TF. Therefore, this two-stage TF system can be employed as a low-cost desulfurization system to perform biogas purification and nitrogen elimination.

Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill.

The activated sludge process within the pulp and paper industry is generally run to minimize the production of waste activated sludge (WAS), leading to high electricity costs from aeration and relatively large basin volumes. In this study, a pilot-scale activated sludge process was run to evaluate the concept of treating the wastewater at high rate with a low sludge age. Two 150 L containers were used, one for aeration and one for sedimentation and sludge return. The hydraulic retention time was decreased from 24 hours to 7 hours, and the sludge age was lowered from 12 days to 2-4 days. The methane potential of the WAS was evaluated using batch tests, as well as continuous anaerobic digestion (AD) in 4 L reactors in mesophilic and thermophilic conditions. Wastewater treatment capacity was increased almost four-fold at maintained degradation efficiency. The lower sludge age greatly improved the methane potential of the WAS in batch tests, reaching 170 NmL CH4/g VS at a sludge age of 2 days. In addition, the continuous AD showed a higher methane production at thermophilic conditions. Thus, the combination of high-rate wastewater treatment and AD of WAS is a promising option for the pulp and paper industry.

Mathematical Simulation of the Process of Aerobic Treatment of Wastewater under Conditions of Diffusion and Mass Transfer Perturbations

A mathematical model of the process of aerobic treatment of wastewater has been refined. It takes into account the interaction of bacteria, as well as of organic and biologically nonoxidizing substances under conditions of diffusion and mass transfer perturbations. An algorithm of the solution of the corresponding nonlinear perturbed problem of convection–diffusion–mass transfer type has been constructed, with a computer experiment carried out based on it. The influence of the concentration of oxygen and of activated sludge on the quality of treatment is shown. Within the framework of the model suggested, a possibility of automated control of the process of deposition of impurities in a biological filter depending on the initial parameters of the water medium is suggested.