Assessment of a UASB reactor with high ammonia concentrations: Effect of zeolite addition on process performance

A critical review on bioaugmentation assisted anaerobic digestion for methane production: Performances, microbiome-functionalities and challenges

Bioaugmentation technology is considered as a straightforward approach to improve anaerobic digestion performances, with advantages of high efficiency and sustainability. However, the mechanisms and challenges of bioaugmentation in anaerobic digestion have yet to been well reviewed. In this review, the advantages of bioaugmentation in anaerobic digestion are systematically identified and discussed, covering enhancing anaerobic digestion process, relieving toxic inhibition of ammonia, and overcoming limitation of psychrophilic anaerobic digestion. This review find that the underlying mechanisms of bioaugmentation enhancing anaerobic digestion are the improvement of microbial community metabolism activity, interspecies electron transfer, and microbial adaptability to environment stress. In addition, future challenges and research directions are discussed from theoretical and practical perspectives, including preparation of bioaugmentation microorganisms, immobilization of bioaugmentation microorganisms, and economic feasibility of bioaugmentation technology. This review contributes to understanding the positive effect of bioaugmentation on anaerobic digestion and promoting the applicability of bioaugmentation technology in anaerobic digestion.

Unifying concepts in methanogenic, aerobic, and anammox sludge granulation

The retention of dense and well-functioning microbial biomass is crucial for effective pollutant removal in several biological wastewater treatment technologies. High solids retention is often achieved through aggregation of microbial communities into dense, spherical aggregates known as granules, which were initially discovered in the 1980s. These granules have since been widely applied in upflow anaerobic digesters for waste-to-energy conversions. Furthermore, granular biomass has been applied in aerobic wastewater treatment and anaerobic ammonium oxidation (anammox) technologies. The mechanisms underpinning the formation of methanogenic, aerobic, and anammox granules are the subject of ongoing research. Although each granule type has been extensively studied in isolation, there has been a lack of comparative studies among these granulation processes. It is likely that there are some unifying concepts that are shared by all three sludge types. Identifying these unifying concepts could allow a unified theory of granulation to be formed. Here, we review the granulation mechanisms of methanogenic, aerobic, and anammox granular sludge, highlighting several common concepts, such as the role of extracellular polymeric substances, cations, and operational parameters like upflow velocity and shear force. We have then identified some unique features of each granule type, such as different internal structures, microbial compositions, and quorum sensing systems. Finally, we propose that future research should prioritize aspects of microbial ecology, such as community assembly or interspecies interactions in individual granules during their formation and growth.

A review on upflow anaerobic sludge blanket reactor: Factors affecting performance, modification of configuration and its derivatives

The upflow anaerobic sludge blanket (UASB) reactor can be considered as one of the promising anaerobic wastewater treatment technologies suitable for the treatment of high-strength wastewater. In the recent period, researchers have focused on the treatment of low-strength wastewater using this technology. This review focuses on the key factors affecting the reactor performance such as hydraulic retention time (HRT), temperature, organic loading rate (OLR), pH and alkalinity, granulation, wastewater characteristics, mixing, and modification to conventional configuration. Start-up and granulation played a major role in the determination of reactor performance, and various theories have been proposed to understand the mechanism of granulation. Correlation between start-up time and OLR was found to be low, as other operating parameters might have been influencing the start-up time. Flowchart depicting the development of UASB reactor over time is included. In the present work, further development and derivatives of the UASB reactor such as static granular bed reactor (SGBR) and expanded granular sludge bed (EGSB) reactor are analyzed. The optimal conditions for UASB for treating various types of substrates was found to be HRT of 3-24 h, OLR of 1-15 kg COD/m³ /d, and operational temperature in mesophilic range (30-40°C). Analysis of various modifications that pave the way for identification of future areas of research to improve reactor performance is also presented.

Operational parameters influenced on biogas production in zeolite/anaerobic baffled reactor for compost leachate treatment

Nowadays, anaerobic processes are used for leachate treatment and biogas production that can be used as a source of renewable and eco-friendly energy. However, for optimal performance of the anaerobic system for gas production, an appropriate method must be used to reduce the inhibitors in the leachate. In this study an anaerobic baffled reactor (ABR) was used for investigating impact of OLR on biogas production and changes of alkalinity and pH. In order to decline inhibitors concentration on anaerobic microorganisms, zeolite was considered as a media and changes of biogas production was surveyed in different filling ratios. The highest produced biogas at the filling ratios of 10 %, 20 and 30 % were 0.6, 0.63 and 0.9 L/day, respectively and OLR increasing resulted in increase in produced biogas. The values of alkalinity and pH remained in the optimum range for methanogenic bacteria. In all three filling ratios, concentration of ammonia increased with increasing organic loading rate but it has not adverse effect on biogas production. Despite of high concentration of heavy metals, anaerobic baffled reactor with zeolite provided suitable condition for anaerobic microorganisms and biogas production.

Evaluation of a zeolite/anaerobic buffled reactor hybrid system for treatment of low bio-degradable effluents

The main objective of this work was to reduce the inhibitory effects of high contents of organics, ammonia, and heavy metals in an anaerobic buffled reactor (ABR), and to prevent the sludge wash-out using zeolites as media. In this work, a pilot scale of ABR with 8 compartments and a working volume of 14.4 L was used, and the last four ABR compartments were filled with a zeolite. The bioreactor was operated at HRTs of 3, 4, and 5 days, zeolite filling ratios of 10, 20, and 30%, and influent chemical oxygen demand (COD) concentrations of 10,000, 20,000, and 30,000 mg/L. The results obtained showed that the maximum removal efficiencies of COD and BOD₅ reached 78 and 68%, respectively. The maximum removal was observed at a HRT of 5 days, a 30% medium filling ratio, and a COD of 10,000 mg/L. Increasing the filling ratio in the reactor increased the removal efficiencies of COD and BOD₅ but increasing the concentration of the influent COD and decreasing HRT reduced the removal efficiency of the reactor. The initial BOD₅/COD ratio was equal to 0.36, which increased by 46% when the medium filling ratio was elevated to 30%. The maximum biogas yield was 0.23 L/g of COD_Removed, and the specific methanogenic activity test verified the toxicity effect of the leachate on the gas-producer organisms. The results of scanning electronic microscopy and EDS showed that the zeolite medium immobilized the microorganisms and a biofilm was formed. Also the zeolite, as a well-known ion exchanger, decreased the concentrations of the major inhibitors (ammonia and heavy metals) and improved the reactor efficiency.

Anaerobic digestion of wastewater rich in sulfate and sulfide: effects of metallic waste addition and micro-aeration on process performance and methane production

This work explores the effect of two metallic wastes (mining wastes, MW; fly ashes, FA) and micro-aeration (MA) on the anaerobic digestion of wastewater which is rich in sulfate and sulfide. Two initial COD concentrations (5,000 and 10,000 mg/L) were studied under both conditions in batch systems at 35 °C, with a fixed COD/SO₄^2- ratio = 10, with 100 mg/L of S^2-. It was observed that the use of MW and FA in the assays with an initial COD concentration of 10,000 mg/L resulted in a simultaneous increase in COD removal, sulfate removal, sulfide removal and methane generation, while MA only improved the COD and sulfide removals in comparison with the control system. On the contrary, the use of MW, FA or MA in systems with initial COD concentrations equal to or lower than 5,000 mg/L did not show any improvement with respect to the control system in terms of COD removal, sulfate removal or methane generation, with only sulfide removal being positively affected by MW and FA.

Developing an anaerobic digester with external Zeolite filled column for enhancing methane production from swine manure - A feasibility study

Development of digesters with an external zeolite column facilitates the convenient removal of the zeolite with TAN, without disturbing the continuous anaerobic digestion process. A digester with an inside zeolite bed (In-Zeo) and digester without adding zeolite (No-Zeo) were employed to compare the process performance with digester with external zeolite column (EX-Zeo). The cumulative, CH₄ yields were 5% and 15% greater in the EX-Zeo, and the In-Zeo digesters respectively compared to the No-Zeo digesters. Also, the % VS reduction was 49%, 55% and 41%, respectively in the Ex-Zeo, In-Zeo and No-Zeo digesters. The results indicated that treatment with 7% zeolite during anaerobic digestion has the potential to improve biodegradation of swine manure. The addition of zeolite appeared to reduce TAN from the digestate, thereby enhancing the CH₄ yield. Zeolite could be used either internally or externally to enhance CH₄ production through anaerobic digestion of swine manure.

Performance and stability of an expanded granular sludge bed reactor modified with zeolite addition subjected to step increases of organic loading rate (OLR) and to organic shock load (OSL)

This paper shows the effect of organic shock loads (OSLs) on the anaerobic digestion (AD) of synthetic swine wastewater using an expanded granular sludge bed (EGSB) reactor modified with zeolite. Two reactors (R1 and R2), each with an effective volume of 3.04 L, were operated for 180 days at a controlled temperature of 30 °C and hydraulic retention time of 12 h. In the case of R2, 120 g of zeolite was added. The reactors were operated with an up-flow velocity of 6 m/h. The evolution of pH, total Kjeldahl nitrogen, chemical oxygen demand (COD) and volatile fatty acids (VFAs) was monitored during the AD process with OSL and increases in the organic loading rate (OLR). In addition, the microbial composition and changes in the structure of the bacterial and archaeal communities were assessed. The principal results demonstrate that the presence of zeolite in an EGSB reactor provides a more stable process at higher OLRs and after applying OSL, based on both COD and VFA accumulation, which presented with significant differences compared to the control. Denaturing gradient gel electrophoresis band profiles indicated differences in the populations of Bacteria and Archaea between the R1 and R2 reactors, attributed to the presence of zeolite.

An enhanced anaerobic membrane bioreactor treating bamboo industry wastewater by bamboo charcoal addition: Performance and microbial community analysis

In this study, two anaerobic membrane bioreactors (AnMBRs) were operated for 150days to treat bamboo industry wastewater (BIWW), and one of them was enhanced with bamboo charcoal (B-AnMBR). During the steady period, average chemical oxygen demand (COD) removal efficiencies of 94.5±2.9% and 89.1±3.1% were achieved in B-AnMBR and AnMBR, respectively. The addition of bamboo charcoal (BC) increased the amount of biomass and improved the performance of the systems. A higher biogas production and methane yield were also observed in B-AnMBR. Regarding the issue of membrane fouling, BC lowered the soluble microbial product (SMP) content by approximately 62.73mg/L and decreased the membrane resistance, thereby mitigating membrane fouling. Analysis of the microbial communities demonstrated that BC increased the microbial diversity and promoted the activity of Methanosaeta, Methanospirillum, and Methanobacterium, which are dominant in methane production.

Influence of Membrane Materials and Operational Modes on the Performance of Ultrafiltration Modules for Drinking Water Treatment

Polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN) were prepared to purify micropolluted source water via a pilot-plant test. Integrative devices of in-line coagulation/ultrafiltration (UF) were proposed. Then the treatment performance, operation stability, clean methods, and fresh water recovery rate were assessed. The results showed that the membrane materials and operational modes did not result in significant difference of the removal efficiency of turbidity,CODMn, and NH4-N. The uniform distribution porosity, better hydrophilicity, and higher thermal stability of the PES membrane made its specific flux (SF) more than double those of two other membranes; in addition, the transmembrane pressure (TMP) of PES membrane appeared to be the least influenced by temperature change. The hydrophilicity of UF membrane was not a conclusive factor with the critical flux. The inside-out module with higher fouling load presented higher decay rate of SF under fixed flux operation compared with outside-in modules in single filtration duration. The way of gas washing of outside-in modules as a supplement resulted in recovery improvement. The acid-base staggered method of inside-out module to carry out chemical enhanced backwash (CEB) can effectively intensify the effects of backwashing by water.

Local-scale recovery of wastewater nitrogen for edible plant growth

An anaerobic/ion exchange (AN-IX) system was developed for recovery and reuse of wastewater nitrogen at point-of-origin. AN-IX combines upflow solids blanket anaerobic treatment with ammonium ion adsorption onto granular natural zeolite. AN-IX operates passively and without energy input. A 57 L empty-bed prototype was operated for 355 days on wastewater primary effluent. Total nitrogen removal exceeded 95% over the first 214 days of operation and ammonia reduction exceeded 99%; accumulation of oxidized nitrogen species (NO3(-) + NO2(-)) was not observed. The wastewater flowrate was increased during the last 35 days of operation to deliberately exhaust the ion exchange media. Spent granular media was removed from the AN-IX prototype and deployed in plant chamber experiments for cultivation of Solanum lycopersicum (cherry tomato). Wastewater nitrogen captured on zeolite was capable of supplying the total growth requirement for nitrogen. Canopy volume and plant flowering and fruiting were higher for wastewater nitrogen than for artificial fertilizer. The AN-IX process is a passive, mechanically simple and reliable system for local-scale nitrogen recovery. AN-IX is modular, scalable, adaptable and can be applied in diverse treatment contexts and recycling scenarios. AN-IX benefits include appropriate technology for local-scale nitrogen recovery, low capital and energy costs, and protection of health and the environment.

Anaerobic-ion exchange (AN-IX) process for local-scale nitrogen recovery from wastewater

An anaerobic-ion exchange (AN-IX) process was developed for point-of-origin recovery of nitrogen from household wastewater. The process features upflow solids-blanket anaerobic treatment (ammonification) followed by ammonium ion exchange onto natural zeolite. The AN-IX system is configured as a series of linked upflow chambers that operate passively without energy input, and is amenable to intermittent and seasonal operation. A 57L prototype was operated for over 1.8 years treating actual wastewater under field conditions. Total nitrogen removal exceeded 96% through the first 160 days of operation and effluent ammonium nitrogen remained below detection for 300 days. Ion exchange chambers exhibited sequential NH4(+)-N breakthrough over extended operation and complete media exhaustion was approached at Day 355. The ammonium capacity of zeolite was estimated as 13.5mg NH4(+)-N per gram dry weight. AN-IX is a resilient and cost effective process for local-scale nitrogen recovery and reuse, suitable for small scale and larger systems.