Effect of natural zeolite on methane production for anaerobic digestion of ammonium rich organic sludge

Impact of additives on syntrophic propionate and acetate enrichments under high-ammonia conditions

High ammonia concentrations in anaerobic degradation systems cause volatile fatty acid accumulation and reduced methane yield, which often derive from restricted activity of syntrophic acid-oxidising bacteria and hydrogenotrophic methanogens. Inclusion of additives that facilitate the electron transfer or increase cell proximity of syntrophic species by flocculation can be a suitable strategy to counteract these problems, but its actual impact on syntrophic interactions has yet to be determined. In this study, microbial cultivation and molecular and microscopic analysis were performed to evaluate the impact of conductive (graphene, iron oxide) and non-conductive (zeolite) additives on the degradation rate of acetate and propionate to methane by highly enriched ammonia-tolerant syntrophic cultures derived from a biogas process. All additives had a low impact on the lag phase but resulted in a higher rate of acetate (except graphene) and propionate degradation. The syntrophic bacteria 'Candidatus Syntrophopropionicum ammoniitolerans', Syntrophaceticus schinkii and a novel hydrogenotrophic methanogen were found in higher relative abundance and higher gene copy numbers in flocculating communities than in planktonic communities in the cultures, indicating benefits to syntrophs of living in close proximity to their cooperating partner. Microscopy and element analysis showed precipitation of phosphates and biofilm formation in all batches except on the graphene batches, possibly enhancing the rate of acetate and propionate degradation. Overall, the concordance of responses observed in both acetate- and propionate-fed cultures highlight the suitability of the addition of iron oxide or zeolites to enhance acid conversion to methane in high-ammonia biogas processes. KEY POINTS: • All additives promoted acetate (except graphene) and propionate degradation. • A preference for floc formation by ammonia-tolerant syntrophs was revealed. • Microbes colonised the surfaces of iron oxide and zeolite, but not graphene.

Natural Ecuadorian zeolite: An effective ammonia adsorbent to enhance methane production from swine waste

Anaerobic digestion (AD) of swine waste allows obtaining renewable energy, biofertilizer and the reduction of environmental impacts. However, the low C:N ratio of pig manure generates high concentrations of ammonia nitrogen in the digestion process, reducing methane production. Zeolite is an effective ammonia adsorbent; thus, in this research the ammonia adsorption capacity of natural Ecuadorian zeolite was studied under different operating conditions. Subsequently, its effect on methane production from swine waste was evaluated using three doses of zeolite, 1.0, 4.0 and 8.0 g, in 1 L batch bioreactors. The results showed that the Ecuadorian natural zeolite has an adsorption capacity of around 19 mgNH₃-N gZ^-1 when using ammonium chloride solution and, an adsorption capacity between 37 and 65 mgNH₃-N gZ^-1 using swine waste. On the other hand, the addition of zeolite had a significant effect on methane production (p < 0.01). The zeolite doses that provided the highest methane production were 4.0 and 8.0 g L^-1, which led to values of 0.375 and 0.365 Nm³CH₄ kgVS^-1, compared to the values of 0.350 and 0.343 Nm³CH₄ kgVS^-1 that were obtained for the treatments without addition of zeolite and using a dose of 1.0 g L^-1, respectively. Addition of natural Ecuadorian zeolite meant not only a significant increase on methane production in the AD of swine waste, but also a better quality of the biogas with higher percentages of methane and lower concentrations of H₂S.

Alleviating "inhibited steady-state" in anaerobic digestion of poultry manure by bentonite amendment: Performance evaluation and microbial mechanism

This study systematically evaluated the effects of bentonite as a possible additive to alleviate the "inhibited steady-state" induced by ammonia and acid accumulation during anaerobic digestion. Continuous stirred tank reactors fed with poultry manure were operated at 35 ± 1 °C either with bentonite or not. The results demonstrate that bentonite amendment increased average specific methane production by 35% as suffered from steady-state at an organic loading rate of 6.25 g VS/L·d. 16S rRNA gene amplicon sequencing revealed that the relative abundance of electron-donating Sedimentibacter and Syntrophomonas, and electrophilic Methanosarcina was increased by 110%, 91%, and 49%, respectively. The genera were identified as crucial for alleviating "inhibited steady-state", through establishment of a more robust syntrophic pathway of methanogenic acetate degradation. The enhancement might result from the accelerated electron transfer by bentonite, which is qualified for serving as an exogenetic electron mediator due to containing abundant redox-active metal elements.

Sustainable additives for the regulation of NH3 concentration and emissions during the production of biomethane and biohydrogen: A review

This study reviews the recent advances and innovations in the application of additives to improve biomethane and biohydrogen production. Biochar, nanostructured materials, novel biopolymers, zeolites, and clays are described in terms of chemical composition, properties and impact on anaerobic digestion, dark fermentation, and photofermentation. These additives can have both a simple physical effect of microbial adhesion and growth, and a more complex biochemical impact on the regulation of key parameters for CH₄ and H₂ production: in this study, these effects in different experimental conditions are reviewed and described. The considered parameters include pH, volatile fatty acids (VFA), C:N ratio, and NH₃; additionally, the global impact on the total production yield of biogas and bioH₂ is reviewed. A special focus is given to NH₃, due to its strong inhibition effect towards methanogens, and its contribution to digestate quality, leaching, and emissions into the atmosphere.

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.

Electrochemical Ammonia Recovery from Anaerobic Centrate Using a Nickel-Functionalized Activated Carbon Membrane Electrode

Ammonia (NH₃) recovery from used water (previously wastewater) is highly desirable to depart from fossil fuel-dependent NH₃ production and curb nitrogen emission to the environment. Electrochemical NH₃ recovery is promising since it can simply convert aqueous NH₄⁺ to gaseous NH₃ using cathodic reactions (OH^- generation). However, the use of a separated electrode and membrane imposes high resistances to the cathodic reaction and NH₃ transfer. This study examined an activated carbon (AC)-based membrane electrode functionalized with nickel to electrochemically recover NH₃ from synthetic anaerobic centrate. The membrane electrode was fabricated using nickel-adsorbed AC powder and a polyvinylidene fluoride (PVDF) binder, and the PVDF membrane layer was formed at the electrode surface by phase inversion. The NH₃-N recovery flux of 50.3 ± 0.4 gNH₃-N/m²/d was produced at 17.1 A/m² with a recovery solution at pH 7, and NH₃-N fluxes and energy consumptions were improved as the recovery solution became acidic (62.2 ± 2.1 gNH₃-N/m²/d with 16.0 ± 1.6 kWh/kgNH₃-N at pH 2). Increasing PVDF loadings did not impact the electrochemical performances of the Ni/AC-PVDF electrode, but slightly lower (7%) NH₃-N fluxes were obtained with higher PVDF loadings. Ni dissolution (3.7-6.0% loss) was affected by the recovery solution pH, but it did not impact the performances over the cycles.

Zeolite favours propionate syntrophic degradation during anaerobic digestion of food waste under low ammonia stress

Zeolite addition has been widely suggested for its ability to overcome ammonia stress occurring during anaerobic digestion. However little is known regarding the underlying mechanisms of mitigation and especially how zeolite influences the microbial structuration. The aim of this study was to bring new contributions on the effect of zeolite on the microbial community arrangement under a low ammonia stress. Replicated batch experiments were conducted. The microbial population was characterised with 16S sequencing. Methanogenic pathways were identified with methane isotopic fractionation. In presence of ammonia, zeolite mitigated the decrease of biogas production rate. Zeolite induced the development of Izimaplasmatales order and preserved Peptococcaceae family members, known as propionate degraders. Moreover methane isotopic fractionation showed that hydrogenotrophic methanogenesis was maintained in presence of zeolite under ammonia low stress. Our results put forward the benefit of zeolite to improve the bacteria-archaea syntrophy needed for propionate degradation and methane production under a low ammonia stress.

Effect of Clinoptilolite and Halloysite Addition on Biogas Production and Microbial Community Structure during Anaerobic Digestion

The study presents a comparison of the influence of a clinoptilolite-rich rock-zeolite (commonly used for improving anaerobic digestion processes)-and a highly porous clay mineral, halloysite (mainly used for gas purification), on the biogas production process. Batch experiments showed that the addition of each mineral increased the efficiency of mesophilic anaerobic digestion of both sewage sludge and maize silage. However, halloysite generated 15% higher biogas production during maize silage transformation. Halloysite also contributed to a much higher reduction of chemical oxygen demand for both substrates (by ~8% for maize silage and ~14% for sewage sludge) and a higher reduction of volatile solids and total ammonia for maize silage (by ~8% and ~4%, respectively). Metagenomic analysis of the microbial community structure showed that the addition of both mineral sorbents influenced the presence of key members of archaea and bacteria occurring in a well-operated biogas reactor. The significant difference between zeolite and halloysite is that the latter promoted the immobilization of key methanogenic archaea Methanolinea (belong to Methanomicrobia class). Based on this result, we postulate that halloysite could be useful not only as a sorbent for (bio)gas treatment methodologies but also as an agent for improving biogas production.

Effect of zero-valent iron combined with carbon-based materials on the mitigation of ammonia inhibition during anaerobic digestion

Ammonia inhibition is a prominent problem for anaerobic digestion (AD) of nitrogen-rich organic wastes. This study evaluated the effect of zero valent iron (ZVI) and its hybrid with activated carbon (AC), graphite and Fe-C material on the mitigation of ammonia inhibition under ammonia concentration over 5 g/L, according to the batch mode experiments. Results showed that ZVI (4 g/L) and its hybrid with carbon-based material preserving methane production from ammonia inhibition, with kinetics of shortening lag phase from 4.77 d to 2.62 d or even below 2 d with carbon-based material. ZVI preserved methane production with the enrichment of Methanosarcina (the relative abundance was over 80%), which was mostly derived from the activating hydrogenotrophic methanogenesis through the enhanced DIET but not the changes of ORP and FAN.

Exploring Biogas and Biofertilizer Production from Abattoir Wastes in Nigeria Using a Multi-Criteria Assessment Approach

Management of waste streams from abattoirs is a major challenge in developing countries. Harnessing these wastes as resources for the production of biogas and biofertilizer could contribute to curbing the environmental menace and to addressing the problems of energy and food deficits in Nigeria. However, large scale uptake of the technology is faced with techno-socio-economic and the lack of data required for effective investment decisions. In this study, the potential use of waste generated in the north central region of Nigerian abattoirs, representing approximately 12% of the land and 6% of the population, were evaluated for suitability for biogas and biofertilizer production. Data acquired from the study sites were used for computational estimation and integrated into strengths, weaknesses, opportunities, and threats (SWOT) analysis to give a detailed overview of the prospects and the limiting factors. The study revealed that high investment costs and public subsidies for fossil fuels are the key limiting factors while the prospects of tapping into the unexploited carbon markets and multiple socio-economic and environmental benefits favors investment. Public supports in the form of national policy reforms leading to intervention programs are required for progress.

Coupling electrochemical ammonia extraction and cultivation of methane oxidizing bacteria for production of microbial protein

Conventional treatment of residual resources relies on nutrient removal to limit pollution. Recently, nutrient recovery technologies have been proposed as more environmentally and energetically efficient strategies. Nevertheless, the upcycling of recovered resources is typically limited by their quality or purity. Specifically, nitrogen extracted from residual streams, such as anaerobic digestion (AD) effluents and wastewaters, could support microbial protein production. In this context, this study was performed as a proof-of-concept to combine nitrogen recovery via electrochemical reactors with the production of high quality microbial protein via cultivation of methanotrophs. Two types of AD effluents, i.e., cattle manure and organic fraction of municipal solid waste, and urine were tested to investigate the nitrogen extraction efficiency. The results showed that 31-51% of the nitrogen could be recovered free of trace chemicals from residual streams depending on the substrate and voltage used. Based on the results achieved, higher nitrogen concentration in the residual streams resulted in higher nitrogen flux between anodic and cathodic chambers. Results showed that the extraction process has an energy demand of 9.97 (±0.7) - 14.44 (±1.19) kWh/kg-N, depending on the substrate and operating conditions. Furthermore, a mixed-culture of methanotrophic bacteria could grow well with the extracted nitrogen producing a total dry weight of 0.49 ± 0.01 g/L. Produced biomass contained a wide range of essential amino acids making it comparable with conventional protein sources.

Effect of organic loading rate on anaerobic digestion of pig manure: Methane production, mass flow, reactor scale and heating scenarios

The effect of organic loading rate (OLR) with total solid (TS) control (3%-8%) on the performance of anaerobic digestion of pig manure (PM) using completely stirred anaerobic reactor was investigated. Based on the lab data, how OLR affects mass flow, construction scale and heating requirement in a farm-scale biogas plant was calculated. And three scenarios of typical reactor-heating technology were comparatively analyzed. The optimal OLR was 1.89 g volatile solid (VS)/(L^.d) with methane yield of 438.38 mL/gVS in the lab condition. The lower OLR, the larger amount of water and energy consumption, lower methane production and larger amount of liquid digestate was observed. Thus, the reactor with low OLR was suitable in tropical regions with the main target of disposing PM and fertilizer production. High OLR has advantage in the investment, but owns risk of instable process for a long-term run. In our study, among the three heating supply scenarios, biogas boiler was the best option for the designed biogas plant with the given breeding scale under moderate OLR. Combined heat and power (CHP) has potential advantage for the biogas plant under high OLR.

Carbon dioxide sequestration and methane production promotion by wollastonite in sludge anaerobic digestion

This study investigated the feasibility and performance of simultaneous in-situ CO₂ sequestration and CH₄ production promotion by wollastonite addition in sludge AD. A maximum CH₄ yield increment of 30.8% and maximum methane production rate increment of 64.9% with wollastonite addition at dosage of 16.25 g/L were achieved. CO₂ was efficient sequestered by wollastonite addition and resulted in a higher CH₄ content of 81.7%-82.4%. The mechanism of CO₂ sequestration by wollastonite was confirmed as Ca²⁺ release and subsequently carbonation based on cation and precipitates analysis. The results demonstrated that wollastonite could be applied as an effective additive for simultaneous in-situ CO₂ sequestration and CH₄ production promotion of sludge AD.

Hybrid algal photosynthesis and ion exchange (HAPIX) process for high ammonium strength wastewater treatment

A hybrid algal photosynthesis and ion exchange (HAPIX) process was developed that uses natural zeolite (chabazite) and wild type algae to treat high ammonium (NH₄⁺) strength wastewater. In the HAPIX process, NH₄⁺ is temporarily adsorbed from the liquid, which reduces the free ammonia (FA) concentration below the inhibitory level for algal growth. The slow release of adsorbed NH₄⁺ subsequently supports the continuous growth of algae. In this study, a HAPIX reactor reduced NH₄⁺-N concentrations in centrate from an anaerobic digester from 1180 mg L^-1 to below 10 mg L^-1 without dilution. Chabazite doses of 60 g L^-1 produced more algal biomass, with higher protein and starch contents, than doses of 150 g L^-1 and 250 g L^-1. Approximately 67-70% of fatty acids in the algal biomass harvested from HAPIX reactors were unsaturated. A mathematical framework that couples a homogeneous surface diffusion model with a co-limitation algal kinetic growth model reasonably predicted the algal biomass production and NH₄⁺-N concentrations in the HAPIX reactors. The HAPIX process has the potential to serve a two-fold purpose of high NH₄⁺-N strength wastewater treatment and agricultural or commercial biopolymer production.

Comprehensive analysis of microbial communities in full-scale mesophilic and thermophilic anaerobic digesters treating food waste-recycling wastewater

Microbes were sampled for a year in a full-scale mesophilic anaerobic digester (MD) and a thermophilic anaerobic digester (TD) treating food waste-recycling wastewater (FRW), then microbial community structure, dynamics and diversity were quantified. In the MD, Fastidiosipila, Petrimonas, vadinBC27, Syntrophomonas, and Proteiniphilum were dominant bacterial genera; they may contribute to hydrolysis and fermentation. In the TD, Defluviitoga, Gelria and Tepidimicrobium were dominant bacteria; they may be responsible for hydrolysis and acid production. In the MD, dominant methanogens changed from Methanobacterium (17.1 ± 16.9%) to Methanoculleus (67.7 ± 17.8%) due to the increase in ammonium concentration. In the TD, dominant methanogens changed from Methanoculleus (42.8 ± 13.6%) to Methanothermobacter (49.6 ± 11.0%) due to the increase of pH. Bacteria and archaea were more diverse in the MD than in the TD. These results will guide development of microbial management methods to improve the process stability of MD and TD treating FRW.

The intensified constructed wetlands are promising for treatment of ammonia stripped effluent: Nitrogen transformations and removal pathways

This study investigated the treatment performance and nitrogen removal mechanism of highly alkaline ammonia-stripped digestate effluent in horizontal subsurface flow constructed wetlands (CWs). A promising nitrogen removal performance (up to 91%) was observed in CWs coupled with intensified configurations, i.e., aeration and effluent recirculation. The results clearly supported that the higher aeration ratio and presence of effluent recirculation are important to improve the alkalinity and pollutant removal in CWs. The influent pH (>10) was significantly decreased to 8.2-8.8 under the volumetric hydraulic loading rates of 0.105 and 0.21 d^-1 in the CWs. Simultaneously, up to 91% of NH₄⁺-N removal was achieved under the operation of a higher aeration ratio and effluent recirculation. Biological nitrogen transformations accounted for 94% of the consumption of alkalinity in the CWs. The significant enrichment of δ¹⁵N-NH₄⁺ in the effluent (47-58‰) strongly supports the occurrence of microbial transformations for NH₄⁺-N removal. However, relatively lower enrichment factors of δ¹⁵N-NH₄⁺ (-1.8‰ to -11.6‰) compared to the values reported in previous studies reflected the inhibition effect of the high pH alkaline environment on nitrifiers in these CWs.

Enhancement of microbial density and methane production in advanced anaerobic digestion of secondary sewage sludge by continuous removal of ammonia

Ammonia inhibition mitigation in anaerobic digestion of high solids content of thermally hydrolysed secondary sewage sludge by the NH₄⁺ affinitive clinoptilolite and a strong acid type ion-exchange resin S957 was investigated. Continuous NH₄⁺-N removal was achieved through ion-exchanging at both temperatures with average removals of 50 and 70% for the clinoptilolite and resin dosed reactors, respectively. Approximate 0.2-0.5unit of pH reduction was also observed in the dosed reactors. The synergy of NH₄⁺-N removal and pH reduction exponentially decreased free NH₃ concentration, from 600 to 90mg/L at 43°C, which mitigated ammonia inhibition and improved methane yields by approximately 54%. Microbial community profiling suggested that facilitated by ammonia removal, the improvement in methane production was mainly achieved through the doubling in bacterial density and a 6-fold increase in population of the Methanosarcinaceae family, which in turn improved the degradation of residual volatile fatty acids, proteins and carbohydrates.

Production of Biogas Using Dairy Manure as Feedstock and Rumen Fluid as Inoculum

 Methane gas is a valuable gas that can be used as a source of energy, either used for cooking fuel or small-scale electricity production. The most suitable application of the methane gas is in rural areas which rarely have the source of energy. It can reduce the dependency of using diesel or gasoline in order to obtain electricity. This study focused on the use of dairy manure as the feedstock and the rumen fluid as the innoculant to improve the production of biogas in rural areas application. The amount of rumen fluid and water added were varied to prepare 0 %, 12.5 %, 25 %, 37.5 % and 50 % rumen fluid. Besides that, the pH level was monitored and its effects towards biogas production was discussed. From the experiment, sample with 37.5 % rumen fluid gave the highest biogas production, followed by 50 %, 25 %, 12.5 % and 0 % rumen fluid. The presence Rumen fluids have improved the biogas production for the anaerobic digestion.

Impact of biochar on the anaerobic digestion of citrus peel waste

In this study, the impact of different types of biochar and biochar ratios on the anaerobic digestion of citrus peel waste was investigated. Citrus peel has an inhibitory effect on anaerobic digestion. The presence of biochar had two effects: a reduction in the length of the lag phase and greater production of methane relative to citrus peel waste only incubations. The microbial lag phases decreased with increase in citrus peel to biochar ratios, with 2:1 having the longest lag phase of 9.4days and 1:3, the shortest, with the value of 7.5days. The cumulative methane production in incubations containing biochar and citrus peel ranged from 163.9 to 186.8ml CH4 gVS(-1), while citrus peel only produced 165.9ml CH4 gVS(-1). Examination of the biochar material revealed colonies of putative methanogens. The synergy of d-limonene adsorption and microbial immobilization by biochar appears to improve the performance of anaerobic digestion.

Biochar alleviates combined stress of ammonium and acids by firstly enriching Methanosaeta and then Methanosarcina

This investigation evaluated the effectiveness of biochar of different particle sizes in alleviating ammonium (NH4(+)) inhibition (up to 7 g-N/L) during anaerobic digestion of 6 g/L glucose. Compared to the control treatment without biochar addition, treatments that included biochar particles 2-5 mm, 0.5-1 mm and 75-150 μm in size reduced the methanization lag phase by 23.9%, 23.8% and 5.9%, respectively, and increased the maximum methane production rate by 47.1%, 23.5% and 44.1%, respectively. These results confirmed that biochar accelerated the initiation of methanization during anaerobic digestion under double inhibition risk from both ammonium and acids. Furthermore, fine biochar significantly promoted the production of volatile fatty acids (VFAs). Comparative analysis on the archaeal and bacterial diversity at the early and later stages of digestion, and in the suspended, biochar loosely bound, and biochar tightly bound fractions suggested that, in suspended fractions, hydrogenotrophic Methanobacterium was actively resistant to ammonium. However, acetoclastic Methanosaeta can survive at VFAs concentrations up to 60-80 mmol-C/L by improved affinity to conductive biochar, resulting in the accelerated initiation of acetate degradation. Improved methanogenesis was followed by the colonization of the biochar tightly bound fractions by Methanosarcina. The selection of appropriate biochar particles sizes was important in facilitating the initial colonization of microbial cells.

Prokaryote community dynamics in anaerobic co-digestion of swine manure, rice straw and industrial clay residuals

The aim of this study was to analyze the effect of the addition of rice straw and clay residuals on the prokaryote methane-producing community structure in a semi-continuously stirred tank reactor fed with swine manure. Molecular techniques, including terminal restriction fragment length polymorphism and a comparative nucleotide sequence analyses of the prokaryotic 16S rRNA genes, were performed. The results showed a positive effect of clay addition on methane yield during the co-digestion of swine manure and rice straw. At the digestion of swine manure, the bacterial phylum Firmicutes and the archaeal family Methanosarcinaceae, particularly Methanosarcina species, were predominant. During the co-digestion of swine manure and rice straw the microbial community changed, and with the addition of clay residual, the phylum Bacteroidetes predominated. The new nutritional conditions resulted in a shift in the archaeal family Methanosarcinaceae community as acetoclastic Methanosaeta species became dominant.

Acceleration of aged-landfill stabilization by combining partial nitrification and leachate recirculation: a field-scale study

Leachate recirculation for rapid landfill stabilization can result in the accumulation of high-strength ammonium. An on-site sequencing batch reactor (SBR) was therefore, applied to oxidize the ammonium to nitrite, which was then recirculated to the landfill for denitrification to nitrogen gas. At relatively higher ammonium levels, nitrite accumulated well in the SBR; the nitrite was denitrified stably in the landfill, despite an insufficient biodegradable carbon source in the leachate. As the leachate was recirculated, the methane and carbon dioxide contents produced from the landfill fluctuated, implying that the organic acids and hydrogen produced in the acid production phase acted as the carbon source for denitrification in the landfill. Leachate recirculation combined with ex-situ partial nitrification of the leachate may enhance the biodegradation process by: (a) removing the nitrogen that is contained with the leachate, and (b) accelerating landfill stabilization, because the biodegradation efficiency of landfill waste is increased by supplying sufficient moisture and its byproducts are used as the carbon source for denitrification. In addition, partial nitrification using an SBR has advantages for complete denitrification in the landfill, since the available carbon source is in short supply in aged landfills.

Biogas production improvement and C/N control by natural clinoptilolite addition into anaerobic co-digestion of Phragmites australis, feces and kitchen waste

Anaerobic co-digestion (A co-D) performance of Phragmites australis, feces and kitchen waste with addition of clinoptilolite (one main kind of zeolite) was investigated to evaluate the improvement of biogas/methane production and internal mechanism of nitrogen and organics control. A better biogas/methane production was observed by 10% clinoptilolite (v/v) than bentonite and diatomite, with the shortest lag phase of 0.070d(-1), the max rate of 15.89L/(kgVSday) and ultimate biogas production of 308.2L/kgVS as the modified Gompertz equation predicted. Accordingly, the content of methane in the biogas was increased from 44.10% to 65.30%. Furthermore, the clinoptilolite inhibited the acidification of digestion liquid (optimum pH 7.0-7.5) and enhanced the VFAs (acetic acid, propionic acid and butyric acid) destruction. Moreover, 10% of clinoptilolite optimally enhanced the microbial utilization of Ca(2+)/Mg(2+), controlled the C/N ratio, and improved the biogas production as well as NH3-N/NO3-N inhibition efficiency.

Semi-continuous anaerobic digestion for biogas production: influence of ammonium acetate supplement and structure of the microbial community

BACKGROUND

As an efficient disposal method of food waste, anaerobic digestion (AD) for biogas production is widely used. In order to understand the enhanced efficiency and stability of AD by appropriate amounts of ammonia and volatile fatty acids (NH4 (+)/VFAs), the characteristics of the corresponding microbial community with ammonium acetate supplement were investigated by denatured gradient gel electrophoresis (DGGE) and pyrosequencing analyses of samples, with or without supplement of NH4 (+)/VFAs.

RESULTS

In this study, four different supplement strategies of adding ammonium acetate were investigated, including a blank group (without supplement of ammonium acetate), a low group (L group, 0.7 g/L/d), a moderate group (M group, 1.0 g/L/d) and a high group (H group, 1.3 g/L/d), respectively. The average daily gas production was 1,839 mL/d, 1,655 mL/d, 1,448 mL/d and 1,488 mL/d for L, M, H and blank groups, respectively. The results reveal that the absence or overload of NH4 (+)/VFAs leads to the inhibition or failure of the AD operation. The blank and H groups were selected for further investigation of the microbial community by DGGE and pyrosequencing analyses. A significant difference of the microbial communities at different AD stages was observed between the blank and H groups.

CONCLUSIONS

Ammonium acetate, as an efficient supplement, significantly influences the characteristics of a semi-continuous AD operation. The DGGE and pyrosequencing analyses indicated that the different bacterial and archaeal communities occurred in the blank and H groups at different AD stages. Thus, an appropriate ammonium acetate supplement may maintain the balance of the microbial community and could be applied to adjust the AD operation and microbial composition towards optimal biogas production.

Physiological and transcriptomic analyses of the thermophilic, aceticlastic methanogen Methanosaeta thermophila responding to ammonia stress

The inhibitory effects of ammonia on two different degradation pathways of methanogenic acetate were evaluated using a pure culture (Methanosaeta thermophila strain PT) and defined co-culture (Methanothermobacter thermautotrophicus strain TM and Thermacetogenium phaeum strain PB), which represented aceticlastic and syntrophic methanogenesis, respectively. Growth experiments with high concentrations of ammonia clearly demonstrated that sensitivity to ammonia stress was markedly higher in M. thermophila PT than in the syntrophic co-culture. M. thermophila PT also exhibited higher sensitivity to high pH stress, which indicated that an inability to maintain pH homeostasis is an underlying cause of ammonia inhibition. Methanogenesis was inhibited in the resting cells of M. thermophila PT with moderate concentrations of ammonia, suggesting that the inhibition of enzymes involved in methanogenesis may be one of the major factors responsible for ammonia toxicity. Transcriptomic analysis revealed a broad range of disturbances in M. thermophila PT cells under ammonia stress conditions, including protein denaturation, oxidative stress, and intracellular cation imbalances. The results of the present study clearly demonstrated that syntrophic acetate degradation dominated over aceticlastic methanogenesis under ammonia stress conditions, which is consistent with the findings of previous studies on complex microbial community systems. Our results also imply that the co-existence of multiple metabolic pathways and their different sensitivities to stress factors confer resiliency on methanogenic processes.

Zeolites relieves inhibitory stress from high concentrations of long chain fatty acids

Protein and fat rich slaughterhouse waste is a very attractive waste stream for the production of biogas because of the high biochemical methane potential of the substrate. The material has however some drawbacks as the sole material for biogas production due to the production of several process disturbing metabolites such as ammonia, sulfides and long chain fatty acids. We can in this work present results that show that zeolites have the potential to relieve inhibitory stress from the presence of long chain fatty acids. Moreover, the results strongly indicate that it is mainly acetic acid consumers that are most negatively affected by long chain fatty acids and that the mechanism of stress relief is an adsorption of long chain fatty acids to the zeolites. In addition to this, it is shown that the effect is immediate and that only a small amount of zeolites is necessary to cancel the inhibitory effect of long chain fatty acids.

Evaluation of a Ca-modified porphyritic andesite for ammonium removal in the anaerobic digestion process

In this study, a Ca-modified porphyritic andesite (wheat-rice-stone (WRS)) was developed for the anaerobic digestion of ammonium-rich wastes. The Ca-modified WRS was obtained with integrated Ca-salt treatment and calcination. Scanning electron microscope and Brunauer-Emmett-Teller surface area analyses were performed to characterize the Ca-modified WRS, and adsorption isotherms and kinetics were investigated to clarify the adsorption mechanism. The ammonium adsorption process was explained well with a pseudo-second-order kinetic model. The specific surface area of the Ca-modified WRS was determined to be 4.56 sq. m/g, and the maximum NH4(+)-N adsorption capacity was determined to be 45.45 mg/g. These values are improvements over those of natural WRS. The ammonium adsorption capacity remained constant at a pH range from 5.0 to 9.0, which indicates that Ca-modified WRS is a promising material for various applications. The methane-production and chemical oxygen demand-removal aspects of anaerobic digestion were much improved with the addition of Ca-modified WRS. Therefore, Ca-modified WRS could be developed into a viable ammonium adsorbent for the anaerobic digestion of ammonium-rich wastes.

Electrochemical resource recovery from digestate to prevent ammonia toxicity during anaerobic digestion

Ammonia inhibition during anaerobic digestion limits the substrate loading rate and endangers process stability. Furthermore, digestates are interesting feedstocks for nutrient recovery. In this lab-scale study, an electrochemical cell was used to investigate the NH(4)(+) flux from anode to cathode. Under optimal conditions with synthetic wastewater, an NH(4)(+) charge transfer efficiency of 96% and NH(4)(+) flux of 120 g N m(-2) d(-1) could be obtained at a concomitant electricity input of 5 kWh kg(-1) N removed. A more selective NH(4)(+) transfer could be established by maintaining a high concentration of other cations in the cathode compartment. Comparable NH(4)(+) fluxes could be obtained with digestate at an electrical power input of 13 kWh kg(-1) N removed and 41% current efficiency. The ammonium level in the digestate could be lowered from 2.1 to 0.8 - 1.2 g N L(-1). Interestingly, also potassium fluxes of up to 241 g K(+) m(-2) d(-1) could be obtained at 23% current efficiency. As the cathode can be operated at high pH without the need for chemical addition, stripping and absorption of dissolved ammonia could reach 100% efficiency. By valorization of the generated side products, this technology shows economic potential for practical application.

Early warning indicators for process failure due to organic overloading by rapeseed oil in one-stage continuously stirred tank reactor, sewage sludge and waste digesters

Early warning indicators for process failures were investigated to develop a reliable method to increase the production efficiency of biogas plants. Organic overloads by the excessive addition of rapeseed oil were used to provoke the decrease in the gas production rate. Besides typical monitoring parameters, as pH, methane and hydrogen contents, biogas production rate and concentrations of fatty acids; carbon dioxide content, concentrations of calcium and phosphate were monitored. The concentration ratio of volatile fatty acids to calcium acted as an early warning indicator (EWI-VFA/Ca). The EWI-VFA/Ca always clearly and reliably indicated a process imbalance by exhibiting a 2- to 3-fold increase 3-7days before the process failure occurred. At this time, it was still possible to take countermeasures successfully. Furthermore, increases in phosphate concentration and in the concentration ratio of phosphate to calcium also indicated a process failure, in some cases, even earlier than the EWI-VFA/Ca.

Mitigating ammonia inhibition of thermophilic anaerobic treatment of digested piggery wastewater: use of pH reduction, zeolite, biomass and humic acid

High free ammonia released during anaerobic digestion of livestock wastes is widely known to inhibit methanogenic microorganisms and result in low methane production. This was encountered during our earlier thermophilic semi-continuously fed continuously-stirred tank reactor (CSTR) treatment of piggery wastewater. This study explored chemical and biological means to mitigate ammonia inhibition on thermophilic anaerobic treatment of piggery wastewater with the aim to increase organic volatile carbon reduction and methane production. A series of thermophilic anaerobic batch experiments were conducted on the digested piggery effluent to investigate the effects of pH reduction (pH 8.3 to 7.5, 7.0 and 6.5) and additions of biomass (10% v/v and 19% v/v anaerobic digested piggery biomass and aerobic-anaerobic digested municipal biomass), natural zeolite (10, 15 and 20 g/L) and humic acid (1, 5 and 10 g/L) on methane production at 55 °C for 9-11 days. Reduction of the wastewater pH from its initial pH of 8.3 to 6.5 produced the greatest stimulation of methane production (3.4 fold) coupled with reductions in free ammonia (38 fold) and total volatile fatty acids (58% TVFA), particularly acetate and propionate. Addition of 10-20 g/L zeolite to piggery wastewater with and without pH reduction to 6.5 further enhanced total VFA reduction and methane production over their respective controls, with 20 g/L zeolite producing the highest enhancement effect despite the ammonia-nitrogen concentrations of the treated wastewaters remaining high. Without pH reduction, zeolite concentration up to 20 g/L was required to achieve comparable methane enhancement as the pH-reduced wastewater at pH 6.5. Although biomass (10% v/v piggery and municipal wastes) and low humic acid (1 and 5 g/L) additions enhanced total VFA reduction and methane production, they elevated the residual effluent total COD concentrations over the control wastewaters (pH-unadjusted and pH-reduced) unlike zeolite treatment. The outcomes from these batch experiments support the use of pH reduction to 6.5 and zeolite treatment (10-20 g/L) as effective strategies to mitigate ammonia inhibition of the thermophilic anaerobic treatment of piggery wastewater.

Influence of semi-aerobic and anaerobic landfill operation with leachate recirculation on stabilization processes

To investigate the influence of semi-aerobic and anaerobic landfill operation on stabilization processes of landfill sites with leachate recirculation, in situ simulated semi-aerobic landfill sites with leachate recirculation (SLR) and anaerobic landfill sites with leachate recirculation (ALR) were constructed. Refuse properties and landfill settlement were determined. Leachate quality and landfill gas compositions were monitored regularly. Based on the data obtained, leachate quality, landfill gas and final refuse characteristics were adopted as assessment factors to quantitatively evaluate stabilization of landfill sites. The results showed that volatile solids (VS), total organic carbon (TOC) and biologically degradable matter (BDM) of aged refuse in SLR (15.8, 7.3 and 9.9%, respectively) were lower than those in ALR, which were 19.1, 9.2 and 11.3%, respectively. Settlement and reduction ratio of SLR were 1.71 m and 30.91%, respectively, and 1.40 m and 25.45% in the case of ALR. Concentrations of organic pollutants, especially ammonia, were reduced in SLR, and variation in leachate quality was also smoother than ALR. Throughout the experiment the average concentration of CH4 in ALR was higher than that in SLR (36.7 and 14.5%, respectively). At the end of the experiment, SLR was moderately stable, while ALR was moderately unstable. The comprehensive assessment index (I) for SLR and ALR was 200 and 355, respectively.

Study on a fixed zeolite bioreactor for anaerobic digestion of ammonium-rich swine wastes

In this study, a fixed zeolite bioreactor was developed for the anaerobic digestion of ammonium-rich swine wastes (NH(4)(+)-N=3770 mg/l). To investigate the performance of the reactor, a sunken zeolite bioreactor and a bioreactor without zeolite were used as controls. The new bioreactor exhibited good performance, with startup time on the 14th day and methane production of 178.5 ml/g-VS during all 32 days of the experiment at 35°C. This bioreactor significantly shortened startup time, enhanced methane gas yield more than twofold and made COD removal more efficient than under the other models. Furthermore, it reduced the inhibition of high ammonium concentration during the anaerobic digestion of ammonium-rich swine wastes via effective ammonium removal and the immobilisation of microorganisms. Because of its simple structure and good performance, the fixed zeolite bioreactor can be recommended for future use.

The impact of ammonia nitrogen concentration and zeolite addition on the specific methanogenic activity of granular and flocculent anaerobic sludges

This work presents the effect of ammonia nitrogen concentration and zeolite addition on the specific methanogenic activity (SMA) of different anaerobic sludges with various physical structures (granular and flocculent), operating in batch conditions. Piggery, malting production and urban sludges derived from full-scale anaerobic reactors were tested in the experiment as the source of inoculum in batch digesters. It was found that piggery sludge was the most affected by the increase of ammonia nitrogen concentration while malting producing and municipal sludges were less affected. In general, the addition of zeolite at doses in the range of 0.01-0.1 g/g VSS reduced the inhibitory effect of N-NH(4)(+) for piggery sludge (P.S.). For this sludge, the propionic:acetic ratio increased when the concentration of N-NH(4)(+) increased, indicating that methanogenesis was affected. Finally, a study of the microbial population involved in this study for P.S. by using 16S rRNA based molecular techniques revealed a presence of microorganisms following the order: Methanococcaceae > Methanosarcina > Methanosaeta.

Comparison on the removal of phthalic acid diesters in a bioreactor landfill and a conventional landfill

The removal of phthalic acid diesters (PAEs) in municipal solid waste (MSW) from two simulated landfill reactors was compared. The results showed that the original concentrations of dimethyl phthalate (DMP), dibutyl phthalate (DBP) and dioctyl phthalate (DOP) in the refuse were 3.3 microg g(-1), 18.5 microg g(-1) and 0.8 microg g(-1), respectively. The concentrations of DMP and DBP in both leachate and refuse decreased greatly during decomposition of the waste in both reactors. The major loss of PAEs from the landfill occurred during an active methanogenic environment with a low concentration of volatile fatty acids (VFA) in the later period. In addition, strong correlations were found between the residual DMP, DBP concentrations and the biologically degradable material (BDM) of the refuse. Finally, PAEs degraded more rapidly in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill with direct leachate discharge.

Kinetics of anaerobic degradation of screened dairy manure by upflow fixed bed digesters: effect of natural zeolite addition

The effect of the hydraulic retention time (HRT) on the performance of two up-flow anaerobic fixed bed digesters (UFAFBDs) packed with waste tire rubber (D1) and waste tire rubber and zeolite (D2) as micro-organism immobilization supports was studied. It was found that a first-order kinetic model described well the experimental results obtained. The kinetic constants for COD, BOD5, total solids (TS) and volatile solids (VS) removal were determined to be higher in digester D2 than in digester D1 or control. Specifically, they were 0.28 +/- 0.01, 0.32 +/- 0.02, 0.16 +/- 0.01 and 0.24 +/- 0.01 d(- 1) respectively for D1 and 0.33 +/- 0.02, 0.40 +/- 0.02, 0.21 +/- 0.01 and 0.28 +/- 0.01 d(- 1) respectively for D2. This was significant at the 95% confidence level. In addition, the first-order model was also adequate for assessing the effect of the HRT on the removal efficiency and methane production. Maximum methane yield and the first-order constant for methane production were determined and the results obtained were comparable with those obtained by other authors but operating at higher HRTs. Maximum methane yields and the kinetic constant for methane production were 11.1% and 29.4% higher in digester D2 than in D1.

Biomethanation of poultry litter leachate in UASB reactor coupled with ammonia stripper for enhancement of overall performance

In the present study possibility of coupling stripper to remove ammonia to the UASB reactor treating poultry litter leachate was studied to enhance the overall performance of the reactor. UASB reactor with stripper as ammonia inhibition control mechanism exhibited better performance in terms of COD reduction (96%), methane yield (0.26m(3)CH(4)/kg COD reduced), organic loading rate (OLR) (18.5kg COD m(-3)day(-1)) and Hydraulic residence time (HRT) (12h) compared to the UASB reactor without stripper (COD reduction: 92%; methane yield: 0.21m(3)CH(4)/kg COD reduced; OLR: 13.6kg CODm(-3)day(-1); HRT: 16h). The improved performance was due to the reduction of total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) in the range of 75-95% and 80-95%, respectively by the use of stripper. G/L (air flow rate/poultry leachate flow rate) in the range of 60-70 and HRT in the range of 7-9min are found to be optimum parameters for the operation of the stripper.

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.

Treatment of wastewater from red and tropical fruit wine production by zeolite anaerobic fluidized bed reactor

A study of the anaerobic treatment of wastewaters derived from red (RWWW) and tropical fruit wine (TFWWW) production was carried out in four laboratory-scale fluidized bed reactors with natural zeolite as bacterial support. These reactors operated at mesophilic temperature (35 degrees C). Reactors R1 and R2 contained Chilean natural zeolite, while reactors R3 and R4 used Cuban natural zeolite as microorganism support. In addition, reactors R1 and R3 processed RWWW, while reactors R2 and R4 used TFWWW as substrate. The biomass concentration attached to zeolites in the four reactors studied was found to be in the range of 44-46 g volatile solids (VS)/L after 90 days of operation time. Both types of zeolites can be used indistinctly in the fluidized bed reactors achieving more than 80%-86% chemical oxygen demand (COD) removals for organic loading rates (OLR) of up to at least 20 g COD/L d. pH values remained within the optimal range for anaerobic microorganisms for OLR values of up to 20 and 22 g COD/L d for RWWW and TFWWW, respectively. Toxicity and inhibition levels were observed at an OLR of 20 g COD/L d in reactors R1 and R3 while processing RWWW, whereas the aforementioned inhibitory phenomena were not observed at an OLR of 24 g COD/L d in R2 and R4, treating TFWWW as a consequence of the lower phenolic compound content present in this substrate. The volatile fatty acid (VFA) levels were always lower in reactors processing TFWWW (R2 and R4) and these values (< 400 mg/L, as acetic acid) were lower than the suggested limits for digester failure. The specific methanogenic activity (SMA) was twice as high in reactors R2 and R4 than in R1 and R3 after 120 days of operation when all reactors operated at an OLR of 20 g COD/L d.

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.

Biogas production from plant biomass used for phytoremediation of industrial wastes

In present study, potentials of water hyacinth (Eichhornia crassipes) and water chestnut (Trapa bispinnosa) employed for phytoremediation of toxic metal rich brass and electroplating industry effluent, were examined in terms of biogas generation. Inability of the plants to grow in undiluted effluent directed to select 20%, 40% and 60% effluent concentrations (with deionized water) for phytoremediation experiments. Slurry of both the plants used for phytoremediation produced significantly more biogas than that by the control plants grown in unpolluted water; the effect being more pronounced with plants used for phytoremediation of 20% effluent. Maximum cumulative production of biogas (2430c.c./100gdm of water hyacinth and 1940c.c./100gdm of water chest nut) and per cent methane content (63.82% for water hyacinth and 57.04% for water chestnut) was observed at 5mm particle size and 1:1 substrate/inoculum ratio, after twenty days incubation. Biogas production was quicker (maximum from 8-12days) in water hyacinth than in water chestnut (maximum from 12-16days). The qualitative and quantitative variations in biogas production were correlated with COD, C, N, C/N ratio and toxic metal contents of the slurry used.