High-rate Anaerobic Systems Research Articles

Application of biomagnetic nanoparticles for biostimulation of biogas production from wastewater treatment

This study presents biomagnetic nanoparticles (BMNPs) as a biostimulant for wastewater treatment and biogas upgrading to natural quality (>90% CH4). Notwithstanding, application of anaerobic digestion (AD) in wastewater settings is still limited with slow kinetics and low methanation yield. Here, four BMNPs (CuO, Fe2O3, TiO2, Cu/Fe-TiO2) were investigated to enhance the high-rate anaerobic system for complete degradation of organic waste to value – added products (water and biogas). Sugar refinery wastewater was used as a substrate and activated sludge as inoculum. This was carried out in 800 mL working volume bioreactors at a mesophilic temperature of 35 °C and hydraulic retention time of 30 days. Results showed the substrate – inoculum degradation in the control system, when induced with the BMNPs increased the methane (CH4) potential from 63% to 100%. Likewise over 75% water index of chemical oxygen demand, total suspended solids, and volatile solids were removed. Stimulatingly, the biogas production and wastewater treatability was significantly improved upon adding the BMNPs to the bioreactors which enriched the methanogenic activities. The post-sludge analysis showed the morphological and elemental distribution of the BMNPs, and their biomagnetic interactions with the micobes which enhanced the adsorptive removal of the contaminants and the biogas production yield. The Gompertz modified kinetic model significantly (P < 0.05) favoured the cumulative biogas yield obtained for all the bioreactors with a kinetic rate constant within the range of 0.182504–0.203027 d-1. The performance of Cu/Fe-TiO2 additives superseded the rest of the BMNPs. In conclusion, BMNPs revealed economic prospects of regeneration and reuse with external magnets for effective wastewater treatment.

Can microaeration boost the biotransformation of parabens in high-rate anaerobic systems?

The main objective of the present study was to demonstrate microaeration as an effective strategy to boost the biotransformation of four parabens (methylparaben, ethylparaben, propylparaben, and butylparaben) in an upflow anaerobic sludge blanket reactor operated at a short hydraulic retention time (8 h). Moreover, the effect of different airflow rates (1−4 mL min−1) was also assessed from an engineering and microbiological perspective. Low mean removal efficiencies (REs) (14–20 %) were achieved under anaerobic conditions. However, the addition of only 1mL air min−1 (0.027L O2L−1 feed) remarkably boosted the biotransformation of parabens, ensuring mean REs above 85 % for all compounds. In contrast, the increase in the airflow rate had a minor impact on the process, and an apparent saturation in the removal capacity was observed, noticeably from 2 to 4 mL air min−1. The reactor presented high stability throughout the experiment, and microaeration did not impair the organic matter removal and methanogenesis. However, high airflow rates can dilute biogas, compromising its use as a fuel in combined heat and power units. The microaerobic conditions increased both richness and diversity of the reactor’s microbiota, likely favoring the growth of oxygenase-producing microorganisms, which may have played a role in the biotransformation of parabens. Finally, the high REs of parabens reached in the microaerated reactor, a more cost-effective technology, are comparable to those found in high-cost wastewater treatment systems, such as activated sludge and its variants.

An electrode-assisted anaerobic digestion process for the production of high-quality biogas

Biogas is a sustainable, renewable energy source generated from organic waste degradation during anaerobic digestion (AD). AD is applied for treating different types of wastewater, mostly containing high organic load. However, AD practice is still limited due to the low quality of the produced biogas. Upgrading biogas to natural gas quality (>90% CH4) is essential for broad applications. Here, an innovative bio-electrochemically assisted AD process was developed, combining wastewater treatment and biogas upgrading. This process was based on a microbial electrolysis cell (MEC) that produced hydrogen from wastewater at a relatively high efficiency, followed by high-rate anaerobic systems for completing biodegradation of organic matter and an in situ bio-methanation process. Results showed that CH4 production yield was substantially improved upon coupling of the MEC with the AD system. Interestingly, CH4 production yield increase was most notable once circulation between AD and MEC was applied, while current density was not markedly affected by the circulation rates. The microbial community analysis confirmed that the MEC enhanced hydrogen production, leading to the enrichment of hydrogenotrophic methanogens. Thus, directing soluble hydrogen from the MEC to AD is plausible, and has great potential for biogas upgrading, avoiding the need for direct hydrogen harvesting.

Quantitative characterization and analysis of granule transformations: Role of intermittent gas sparging in a super high-rate anaerobic system

Knowledge of leveraging biomass characteristics is essential for achieving a microbial community with a desired structure to optimize anaerobic bioreactor performance. This study investigates the successive granule transformations in a high-rate anaerobic system with intermittent gas sparging and sequential increases in organic loading rates (OLRs), by establishing the correlations between the granule microstructures and reactor operating parameters. Over the course of a 196-day lab-scale trial, the granules were visualized in various stages using scanning electron microscopy, and digital image processing was applied for further quantifying their surface properties. Correlation analyses revealed that irregularities of the granule microstructures (surface properties, specific surface area and pore volume) emerged at stage 4 when the OLR was 13.31 kg COD/m3·day and in stage 5 in the absence of gas sparging. The loading ratio (substrate surface loading to upward velocity) was identified to be the main parameter controlling the granule transformations, and the surface structures were classified into three categories for further interpretation. Confocal laser scanning microscopy analyses showed that the granule core started to hollow out from stage 4. It is also found that a rough granule surface helped accelerate the growth of the granular diameter under gas sparging. Overall, this study not only establish quantitative correlations between the granules microstructures and reactor operating parameters, but also shed light on the use of intermittent gas sparging to control the surface properties of anaerobic granules in high-rate anaerobic bioreactors.

Constructed wetlands and solar-driven disinfection technologies for sustainable wastewater treatment and reclamation in rural India: SWINGS project.

SWINGS was a cooperation project between the European Union and India, aiming at implementing state of the art low-cost technologies for the treatment and reuse of domestic wastewater in rural areas of India. The largest wastewater treatment plant consists of a high-rate anaerobic system, followed by vertical and horizontal subsurface flow constructed wetlands with a treatment area of around 1,900 m2 and a final step consisting of solar-driven anodic oxidation (AO) and ultraviolet (UV) disinfection units allowing direct reuse of the treated water. The implementation and operation of two pilot plants in north (Aligarh Muslim University, AMU) and central India (Indira Gandhi National Tribal University, IGNTU) are shown in this study. The overall performance of AMU pilot plant during the first 7 months of operation showed organic matter removal efficiencies of 87% total suspended solids, 95% 5-day biological oxygen demand (BOD5) and 90% chemical oxygen demand, while Kjeldahl nitrogen removal reached 89%. The UV disinfection unit produces water for irrigation and toilet flushing with pathogenic indicator bacteria well below WHO guidelines. On the other hand, the AO disinfection unit implemented at IGNTU and operated for almost a year has been shown to produce an effluent of sufficient quality to be reused by the local population for agriculture and irrigation.

Anaerobic digesters as a pretreatment for constructed wetlands

The most commonly used pretreatment technologies for constructed wetland (CW) treatment of domestic sewage are septic tanks (ST) and Imhoff tanks (IT). These technologies have frequently suffered from failures and even in normal operation they offer insufficient removal of solids. As a result, combined ST-CW or IT-CW can experience substrate clogging, especially when high organic loads are applied. In the last 7 years, the operation of combined systems using high-rate anaerobic digesters as a pretreatment and CW as a post-treatment has been reported. A review of the literature indicates that CW in these combined systems operates with a similar organic loading rate (on a chemical oxygen demand basis) but with a lower total suspended solid (TSS) loading rate. In these combined systems, the TSS loading rate is 30–50% less than that applied in CW combined with classical pretreatment technologies. A low TSS loading rate could prevent substrate clogging in CW. This work presents the results of different case studies on the treatment of municipal wastewater with high-rate anaerobic systems. Our interest is focused on the capacity of these systems for removing suspended solids, and therefore on their potential as an appropriate pretreatment to avoid clogging in constructed wetlands and to improve efficiency. Average and 95 percentile TSS concentrations of anaerobic treated wastewater were below 60 and 100 mg/l, respectively, for all configurations. Therefore, the use of high rate anaerobic systems as a pretreatment for constructed wetlands could delay gravel bed clogging. Furthermore, according to the level of organic matter removal, anaerobic pretreatment provided a 30–60% reduction in the required wetland area. Both treatment alternatives can be combined to develop low-cost, robust, and long-term systems for treating municipal wastewater.

Anaerobic treatment of sulphate-enriched wastewaters

Anaerobic treatment is increasingly being used by industry in preference to aerobic systems to overcome more stringent legislation regarding the discharge of pollutants into the environment. As high-rate anaerobic systems such as the anaerobic baffled reactor (ABR) gain recognition as effective effluent treatment processes, greater demands are made of the systems. Previous work has shown that the ABR can achieve high carbon removal rates through biomass retention and process stability. However, limited information is available on the treatment of wastewaters containing sulphate in the ABR. As such, the aim of this work was to examine the effects of treating wastewaters with high levels of sulphate in a bench-scale ABR. Experimental work involved the use of an ABR with a 10 litre working volume and eight discrete compartments, run under mesophilic conditions (at 35°C). A baseline feed of 4 g chemical oxygen demand (COD)/1 was supplemented with 0·4 g/l sulphate (a COD: sulphate ratio of 10). This allowed the development of biomass in the reactor that was accustomed to sulphate. Once the reactor was operating at a 20 h hydraulic retention time, the sulphate content of the feed was increased stepwise, resulting in a decrease in the COD: sulphate ratio to a minimum level of 1. Microbiological studies were carried out to evaluate the effect of the extreme sulphate loading conditions on the biomass. The ABR was found to perform well at low influent COD: sulphate ratios. In the front of the ABR where sulphate reduction is expected, specific sulphate reduction rates (kg [Formula: see text] volatile suspended solids per day) were significantly higher than the values suggested by the literature. The results of this work showed the structure of the ABR to be well suited to the treatment of wastewaters with low COD: sulphate ratios.

Anaerobic treatment of sulphate-enriched wastewaters

Anaerobic treatment is increasingly being used by industry in preference to aerobic systems to overcome more stringent legislation regarding the discharge of pollutants into the environment. As high-rate anaerobic systems such as the anaerobic baffled reactor (ABR) gain recognition as effective effluent treatment processes, greater demands are made of the systems. Previous work has shown that the ABR can achieve high carbon removal rates through biomass retention and process stability. However, limited information is available on the treatment of wastewaters containing sulphate in the ABR. As such, the aim of this work was to examine the effects of treating wastewaters with high levels of sulphate in a bench-scale ABR. Experimental work involved the use of an ABR with a 10 litre working volume and eight discrete compartments, run under mesophilic conditions (at 35°C). A baseline feed of 4 g chemical oxygen demand (COD)/1 was supplemented with 0·4 g/l sulphate (a COD: sulphate ratio of 10). This allowed the development of biomass in the reactor that was accustomed to sulphate. Once the reactor was operating at a 20 h hydraulic retention time, the sulphate content of the feed was increased stepwise, resulting in a decrease in the COD: sulphate ratio to a minimum level of 1. Microbiological studies were carried out to evaluate the effect of the extreme sulphate loading conditions on the biomass. The ABR was found to perform well at low influent COD: sulphate ratios. In the front of the ABR where sulphate reduction is expected, specific sulphate reduction rates (kg volatile suspended solids per day) were significantly higher than the values suggested by the literature. The results of this work showed the structure of the ABR to be well suited to the treatment of wastewaters with low COD: sulphate ratios.

SE—Structures and Environment: A Dual-reactor Anaerobic System for Complete Treatment of a Food Processing Waste

Anaerobic technologies are commonly employed for the initial treatment of food processing wastewater; however, they are not typically considered capable of treating wastewater to meet final discharge requirements. To assess the potential of anaerobic technologies to meet discharge requirements, the performance of two dual-reactor high-rate anaerobic systems fed with confectionery wastewater was investigated. The primary reactors in the system were operated at constant hydraulic retention times of 1·6 d. The secondary reactors were operated with hydraulic retention times of 0·8, 1·6, and 3·2 d. The secondary reactors, which were both downflow anaerobic filters, achieved maximum chemical oxygen demand (COD) removal rates when operated at a hydraulic retention time of 1·6 d. The brick-filled downflow anaerobic filter and the plastic-ring-filled downflow anaerobic filter produced average effluent five-day biochemical oxygen demand concentrations of 26 mgl−1 (COD=80 mg l−1) and 36 mg l−(COD=112 mg l−1), respectively. To examine the enhanced stability provided by the sequential reactor approach, the dual-reactor system was overloaded at 3·5 times the normal COD concentration (8000 mg l−1) for an 8 h period. The secondary reactors were able to accommodate the increased organic loading emitted from the primary reactors, maintaining an overall removal efficiency of >994%. The results suggest that full anaerobic treatment of readily degradable food waste streams may be realistic, and that a sequential reactor approach significantly enhances overall process stability.

Stability of High-Rate Anaerobic Systems. I: Performance under Shocks

Three laboratory reactors, that is, an anaerobic fluidized bed reactor, an anaerobic filter, and an upflow anaerobic sludge blanket reactor, of identical size and operated under identical conditions, were studied by focusing on the system stability in the presence of various shocks. The results obtained from various shock tests revealed the differences and similarities between the behaviors of different reactors with respect to different system parameters. The stability of the three reactors subjected to various shocks was compared and ranked based on the examination of the responses of some sensitive system parameters. Gas phase parameters should be combined with liquid phase parameters to explicitly characterize an anaerobic system's operating status.

Stability of High-Rate Anaerobic Systems. II: Fuzzy Stability Index

Based on a fuzzy logic method, fuzzy stability index N was proposed to integrate the complex information contained in various system variables and explicitly indicate the departure of a system from normal state. The instability of a system subjected to a shock could be explicitly revealed by its variance of N. Based on the examination of variance of N, the stability of three high-rate anaerobic reactors in the presence of various shocks was quantitatively compared. The comparison results based on N coincided in general with the conclusions obtained from a direct examination of the reactors' performance, but the N comparison method was proven to be much more convenient and explicit as compared with the method of direct examination of the reactors' performance.

A fast predicting neural fuzzy model for high-rate anaerobic wastewater treatment systems

Based on a conceptual neural fuzzy model developed for anaerobic treatment systems, a fast predicting neural fuzzy model was developed to predict the response of high-rate anaerobic systems to different system disturbances 1 h in advance. The model was applied to three laboratory scale systems, i.e. an anaerobic fluidized bed reactor (AFBR), an anaerobic filter (AF), and an upflow anaerobic sludge blanket (UASB) reactor. In all three cases, the model learned well from the training patterns and exhibited good and fast predictions for the performance of the three systems subjected to a two-fold OLR together with two-fold HLR overload shock. It was proven that neural fuzzy modeling has great adaptability to the variations of system configuration and operation condition. The model is expected to have a great application potential in real time system control.

PH-controlled feed-on-demand for high-rate anaerobic systems

The carbonate and short chain fatty acid (SCFA) buffer subsystems govern the pH and thus the required alkalinity in high-rate anaerobic wastewater treatment systems. By controlling the SCFA concentration through a pH-controlled feed-on-demand system, the required alkalinity is only a function of the partial pressure of carbon dioxide (PCO2), and for non-alkalinity producing substrates, independent of the organic loading rate. This makes the pH-controlled feed-on-demand system a simple and very effective method for minimising the start-up time and improving the reliability of high-rate anaerobic digestion. For maximum sensitivity the controlling pH was measured in a pH region near the bicarbonate equivalence point. This condition was obtained by measuring the pH in a biogas stripped side stream. The concept of pH-controlled feed-on-demand was successfully applied for the start-up and operation of an upflow anaerobic sludge bed (UASB) reactor, using SCFAs as substrate.

Start-Up, Operation, Monitoring and Control of High-Rate Anaerobic Treatment Systems

High-rate anaerobic treatment has emerged as a viable alternative for the treatment of many industrial and municipal wastewaters. A number of different process options have been reduced to practice, although some configurations are clearly more well developed than others. One common thread that links these various processes (principally the Anaerobic Filter, Upflow Anaerobic Sludge Blanket and Expanded/Fluidized Bed Reactors), is the ability to effectively separate solids and hydraulic retention times. This permits design to be based upon the degradative capacity of the anaerobes, not growth rate and results in reduction of treatment times from days (typical for conventional digester systems) to hours. This article compares and contrasts the principles of start-up and operation of these different high-rate anaerobic systems based upon laboratory research and full-scale operating experience gained over the past two decades. The application of anaerobic processes for treatment of certain toxic and hazardous waste streams is just beginning. The limited work performed to date and anticipated future needs for process monitoring and control are also presented in this article.