Leach Bed Research Articles

Start-up of a sequential dry anaerobic digestion of paunch under psychrophilic and mesophilic temperatures

The present laboratory study evaluated the sequential leach bed dry anaerobic digestion (DAD) of paunch under psychrophilic (22°C) and mesophilic (40°C) temperatures. Three leach bed reactors were operated under the mesophilic temperature in sequence at a solid retention time (SRT) of 40d with a new batch started 27d into the run of the previous one. A total of six batches were operated for 135d. The results showed that the mesophilic DAD of paunch was efficient, reaching methane yields of 126.9–212.1mLg−1 volatile solid (VS) and a VS reduction of 32.9–55.5%. The average daily methane production rate increased from 334.3mLd−1 to 571.4mLd−1 and 825.7mLd−1 when one, two and three leach bed reactors were in operation, respectively. The psychrophilic DAD of paunch was operated under a SRT of 100d and a total of three batches were performed in sequence for 300d with each batch starting after completion of the previous one. Improvements in the methane yield from 93.9 to 107.3 and 148.3mLg−1 VS and VS reductions of 24.8, 30.2 and 38.6% were obtained in the consecutive runs, indicating the adaptation of anaerobic microbes from mesophilic to psychrophilic temperatures. In addition, it took three runs for anaerobic microbes to reduce the volatile fatty acid accumulation observed in the first and second trials. This study demonstrates the potential of renewable energy recovery from paunch under psychrophilic and mesophilic temperatures.

Community dynamics and significance of anaerobic protozoa during biomethanation of lignocellulosic waste

The diversity and community dynamics of anaerobic protozoa and their functional role during anaerobic digestion of a typical lignocellulose biomass in a lab scale leach bed coupled UASB reactor is reported in this study. The functional role played by different protozoa during various stages of methanogenesis was analyzed through linear regression analysis of individual protozoon counts with major hydrolytic enzyme activities, volatile fatty acid levels and biogas production. The protozoa community in the digester was represented by ciliates (Metopus, Cyclidium and Colpoda) and flagellates (Rhyncomonas, Menoidium and Bodo). Regression analysis revealed the relationship between total protozoa counts with the activity of cellulase (R2 = 0.71) pectinase (R2 = 0.50) amylase (R2 = 0.53) and xylanase (R2 = 0.34), total volatile fatty acid levels (R2 = 0.86) and biogas production (R2 = 0.78) in the digester. Moreover, it was found that both volatile fatty acid and biogas production is correlated with ciliate and flagellate populations. This study underlines the importance of both ciliates and flagellates in the anaerobic digestion process and, more specifically, the contribution by individual protozoa on hydrolysis, which is the rate limiting stage in anaerobic digestion.

Innovative method for increased methane recovery from two-phase anaerobic digestion of food waste through reutilization of acidogenic off-gas in methanogenic reactor

In this study, the performance of a two-phase anaerobic digestion reactor treating food waste with the reutilization of acidogenic off-gas was investigated with the objective to improve the hydrogen availability for the methanogenic reactor. As a comparison a treatment without off-gas reutilization was also set up. Results showed that acidogenic off-gas utilization in the upflow anaerobic sludge blanket (UASB) reactor increased the methane recovery up to 38.6%. In addition, a 27% increase in the production of cumulative chemical oxygen demand (COD) together with an improved soluble microbial products recovery dominated by butyrate was observed in the acidogenic leach bed reactor (LBR) with off-gas reutilization. Of the increased methane recovery, ∼8% was contributed by the utilization of acidogenic off-gas in UASB. Results indicated that utilization of acidogenic off-gas in methanogenic reactor is a viable technique for improving overall methane recovery.

Selective inhibition of methanogenic archaea in leach bed systems by sodium 2-bromoethanesulfonate

Abstract Lignocellulosic biomass is a feasible feedstock for biogas production through anaerobic digestion. Leaching, as part of a two-stage fermentation concept, is the most meaningful strategy to convert the substrate’s organic carbon compounds into volatile fatty acids (VFA) during acidification. Various chemicals have been investigated so far to enhance the process of acidification by selective inhibition of methanogens. Hardly any of them were evaluated for technical leach bed systems. In order to enhance the process of acidification the inhibitory effect of sodium 2-bromoethanesulfonate (BES) on the activity of methanogens was evaluated. An optimal inhibition concentration of 40 mM BES was found in lab-experiments and was verified in a pilot scale leach bed system, which was fed with urban lignocellulosic biomass. Overall, 2200 g/m 3 of acetic acid were achieved during the leaching process by a one-time addition of BES. As VFA concentration levels were observed to be constant, BES approved suitable.

A vertical flow constructed wetland for the treatment of winery process water and domestic sewage in Ontario, Canada: Six years of performance data

Wine production is a growing industry in the Canadian province of Ontario. Due to the high organic loads and large amount of suspended solids found in winery process water it is important for wineries to adopt sustainable water management practices. Constructed wetlands (CW) have been shown to be a viable option in the warmer climates of the Mediterranean and the western USA but little research has examined their feasibility in the cold climate of Ontario. The purpose of this paper was to assess six years of performance data from a vertical flow CW treating winery process water and domestic sewage at a winery in the Niagara region of Ontario with an average hydraulic loading rate (HLR) of 22.3mmd−1 and an average chemical oxygen demand (COD) surface loading rate (SLR) of 34.0gm2d−1. The CW has four cells, each 101m2, and was designed to treat 16,620Lday−1 of wastewater consisting of winery process water and domestic sewage. The performance data were separated by season to determine the effect of temperature on treatment performance during the colder months. There was little variation in seasonal performance and the average treatment efficiencies over the six-year period were: 99% for COD, 99% for carbonaceous COD, 98% for total suspended solids, 83% for total phosphorous, 94% for total Kjeldahl nitrogen, and 85% ammonium. Effluent nitrate, total coliforms, and Escherichia coli concentrations were also monitored and consistently met the regulatory standards for discharge to a subsurface leaching bed. The CW system proved to be an option for treating winery wastewater.

Biotic and abiotic roles of leachate recirculation in batch mode solid-state anaerobic digestion of cattle manure

Solid state anaerobic digestion, with leachate recirculation, is suitable for exploiting manure with a high solid content. The biotic and abiotic effects of the leachates were studied in lab-scale leach bed reactors (LBRs). LBRs were fed with cow manure and four leachates either biologically active or inert. The biotic impact of leachate was assessed by monitoring the microbial communities in the manure and in the leachates. LBRs with biologically active leachates, regardless to their origin, produced equivalent methane volumes (114.52±19.05 and 99.79±6.4NL/kgVS) while LBRs with inert leachates produced half less methane (60.22±5.71 and 58.87±13.2NL/kgVS) attesting to the biotic role of leachate. Moreover, its beneficial abiotic role is mainly due to its initial nutrient content, pH, and buffering capacity. The microbial community in the manure was strongly involved in methane production, and no transfer of microorganisms from the liquid phase was found (p<0.05).

Remediation of Acid Mine Drainage-Impacted Water

The formation of acid mine drainage (AMD), a highly acidic and metal-rich solution, is the biggest environmental concern associated with coal and mineral mining. Once produced, AMD can severely impact the surrounding ecosystem due to its acidity, metal toxicity, sedimentation and other deleterious properties. Hence, implementations of effective post-mining management practices are necessary to control AMD pollution. Due to the existence of a number of federal and state regulations, it is necessary for private and government agencies to come up with various AMD treatment and/or control technologies. This review describes some of the widely used AMD remediation technologies in terms of their general working principles, advantages and shortcomings. AMD treatment technologies can be divided into two major categories, namely prevention and remediation. Prevention techniques mainly focus on inhibiting AMD formation reactions by controlling the source. Remediation techniques focus on the treatment of already produced AMD before their discharge into water bodies. Remediation technologies can be further divided into two broad categories: active and passive. Due to high cost and intensive labor requirements for maintenance of active treatment technologies, passive treatments are widely used all over the world. Besides the conventional passive treatment technologies such as constructed wetlands, anaerobic sulfate-reducing bioreactors, anoxic limestone drains, open limestone channels, limestone leach beds and slag leach beds, this paper also describes emerging passive treatment technologies such as phytoremediation. More intensive research is needed to develop an efficient and cost-effective AMD treatment technology, which can sustain persistent and long-term AMD load.

Stabilization of fine fraction from landfill mining in anaerobic and aerobic laboratory leach bed reactors

Fine fraction (FF, <20mm) from mined landfill was stabilized in four laboratory-scale leach bed reactors (LBR) over 180days. The aim was to study feasibility of biotechnological methods to treat FF and if further stabilization of FF is possible. Four different stabilization methods were compared and their effects upon quality of FF were evaluated. Also during the stabilization experiment, leachate quality as well as gas composition and quantity were analyzed. The methods studied included three anaerobic LBRs (one without water addition, one with water addition, and one with leachate recirculation) and one aerobic LBR (with water addition). During the experiment, the most methane was produced in anaerobic LBR without water addition (18.0LCH4/kgVS), while water addition and leachate recirculation depressed methane production slightly, to 16.1 and 16.4LCH4/kgVS, respectively. Organic matter was also removed via the leachate and was measured as chemical oxygen demand (COD). Calculated removal of organic matter in gas and leachate was highest in LBR with water addition (59gCOD/kgVS), compared with LBR without water addition or with leachate recirculation (51gCOD/kgVS). Concentrations of COD, ammonium nitrogen and anions in leachate decreased during the experiment, indicating washout mechanism caused by water additions. Aeration increased sulfate and nitrate concentrations in leachate due to oxidized sulfide and ammonium. Molecular weight distributions of leachates showed that all the size categories decreased, especially low molecular weight compounds, which were reduced the most. Aerobic stabilization resulted in the lowest final VS/TS (13.1%), lowest respiration activity (0.9–1.2mgO2/gTS), and lowest methane production after treatment (0.0–0.8LCH4/kgVS), with 29% of VS being removed from FF. Anaerobic stabilization methods also reduced organic matter by 9–20% compared with the initial amount. Stabilization reduced the quantity of soluble nitrogen in FF and did not alter concentration of soluble and insoluble phosphorus, and insoluble nitrogen. All four stabilization methods decreased organic matter and thus are possible stabilization methods for FF, but aerobic treatment was the most efficient in this study.

Effect of organic loading rate on the performance of two-stage anaerobic digestion of the organic fraction of municipal solid waste (OFMSW).

Two-stage anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was carried out: hydrolysis and acidogenesis in a continuous anaerobic hydrolytic leach bed (AHLB) reactor loaded at different rates (Bv = 3.8-7 gVSSL⁻¹d⁻¹) and methanogenesis of leachates, diluted with municipal wastewater in an upflow anaerobic sludge blanket (UASB) reactor at organic loading rates of 6.6-13 gCODLr⁻¹d⁻¹. In the AHLB reactor, 51-76% and 58-71% volatile solids and chemical oxygen demand (COD) removal efficiencies were obtained. During the hydrolysis and acidogenesis phases, the effluents were at pH 4.93, the leachate had a volatile fatty acids concentration of 35 g/L and the biogas was composed only of CO₂. The average methane production in the UASB in the load of 4.4 gVS L⁻¹ d⁻¹ in the AHLB was 3.32 LCH4Lr⁻¹d⁻¹ (yCH4 = 80%), with COD removal efficiency of 95% and methane yield 279 LCH4KgVS⁻¹OFMSW degraded.

Solid state co-fermentation as pretreatment of lignocellulosic palm empty fruit bunch for organic acid recovery and fiber property improvement

Batch co-fermentation of lignocellulosic fiber from oil palm empty fruit bunch (EFB), and pig manure (PM) was carried out in anaerobic leach bed reactors under intermittent flushing mode to improve organic acid production and fiber fuel property. Higher PM addition (%PM), long fermentation time (FT), and long leachate flushing interval (FI) showed positive impacts on hydrolysis yield and acidification yield leading to a higher total volatile fatty acid production. Their relationships were described using multivariate models through three-dimensional response surface plots. Volatile solids release from the EFB fiber after 60-day treatment improved by 6.9 times when %PM and FI increased from 0% and 12 h to 50% and 48 h, respectively. Mild acids produced were able to remove as high as 56.9% of hemicellulose and leach 83.5 ± 4.0% of potassium (K) off the fiber. This also resulted in the increased heating value and lowered K content that could minimize slag formation when used in combustion. Addition of PM also supplemented plant nutrients to the EFB digestate. This study demonstrated that co-fermentation could be one of the pretreatment methods to recover valuable products from EFB and help ease its subsequent transformations.

Determination of methanogenic pathways through carbon isotope (δ13C) analysis for the two-stage anaerobic digestion of high-solids substrates.

This study used carbon isotope (δ(13)C)-based calculations to quantify the specific methanogenic pathways in a two-stage experimental biogas plant composed of three thermophilic leach bed reactors (51-56 °C) followed by a mesophilic (36.5 °C) anaerobic filter. Despite the continuous dominance of the acetoclastic Methanosaeta in the anaerobic filter, the methane (CH4) fraction derived from carbon dioxide reduction (CO2), fmc, varied significantly over the investigation period of 200 days. At organic loading rates (OLRs) below 6.0 gCOD L(-1) d(-1), the average fmc value was 33%, whereas at higher OLRs, with a maximum level of 17.0 gCOD L(-1) d(-1), the fmc values reached 47%. The experiments allowed for a clear differentiation of the isotope fractionation related to the formation and consumption of acetate in both stages of the plant. Our data indicate constant carbon isotope fractionation for acetate formation at different OLRs within the thermophilic leach bed reactors as well as a negligible contribution of homoacetogenesis. These results present the first quantification of methanogenic pathway (fmc values) dynamics for a continually operated mesophilic bioreactor and highlight the enormous potential of δ(13)C analysis for a more comprehensive understanding of the anaerobic degradation processes in CH4-producing biogas plants.

Concentrations of hormones, pharmaceuticals and other micropollutants in groundwater affected by septic systems in New England and New York

Septic-system discharges can be an important source of micropollutants (including pharmaceuticals and endocrine active compounds) to adjacent groundwater and surface water systems. Groundwater samples were collected from well networks tapping glacial till in New England (NE) and sandy surficial aquifer New York (NY) during one sampling round in 2011. The NE network assesses the effect of a single large septic system that receives discharge from an extended health care facility for the elderly. The NY network assesses the effect of many small septic systems used seasonally on a densely populated portion of Fire Island. The data collected from these two networks indicate that hydrogeologic and demographic factors affect micropollutant concentrations in these systems.The highest micropollutant concentrations from the NE network were present in samples collected from below the leach beds and in a well downgradient of the leach beds. Total concentrations for personal care/domestic use compounds, pharmaceutical compounds and plasticizer compounds generally ranged from 1 to over 20μg/L in the NE network samples. High tris(2-butoxyethyl phosphate) plasticizer concentrations in wells beneath and downgradient of the leach beds (>20μg/L) may reflect the presence of this compound in cleaning agents at the extended health-care facility.The highest micropollutant concentrations for the NY network were present in the shoreline wells and reflect groundwater that is most affected by septic system discharges. One of the shoreline wells had personal care/domestic use, pharmaceutical, and plasticizer concentrations ranging from 0.4 to 5.7μg/L. Estradiol equivalency quotient concentrations were also highest in a shoreline well sample (3.1ng/L). Most micropollutant concentrations increase with increasing specific conductance and total nitrogen concentrations for shoreline well samples. These findings suggest that septic systems serving institutional settings and densely populated areas in coastal settings may be locally important sources of micropollutants to adjacent aquifer and marine systems.

Performance of a novel two-phase continuously fed leach bed reactor for demand-based biogas production from maize silage

This study investigated the potential of producing biogas on demand from maize silage using a novel two-phase continuously fed leach bed reactor (LBR) which is connected to an anaerobic filter (AF). Six different feeding patterns, each for 1week, were studied at a weekly average of a volatile solids (VS) loading rate of 4.5gL−1d−1 and a temperature of 38°C. Methane production from the LBR and AF responded directly proportional to the VS load from the different daily feeding and resulted in an increase up to 50–60% per day, compared to constant feeding each day. The feeding patterns had no impact on VS methane yield which corresponded on average to 330Lkg−1. In spite of some daily shock loadings, carried out during the different feeding patterns study, the reactor performance was not affected. A robust and reliable biogas production from stalky biomass was demonstrated.

Geochemistry of CO2 in Steel Slag Leach Beds

Performance data was previously collected from steel slag leach beds (SLBs) being used to treat AMD in southeastern Ohio. During initial analysis of the SLB performance, it was postulated that CO2 geochemistry significantly affected the performance through precipitation of carbonate minerals in the flow paths of the SLB. To verify this postulation, we conducted a further investigation of the CO2 geochemistry in the SLBs, including extended geochemical analyses and additional X-ray diffractometer analyses. Since the primary geochemical reaction of CO2 in SLBs is mineral carbonation with calcium, a simple model was used to calculate the Ca dissolution potentials in the SLBs. The molar values for Ca dissolution potential were then used along with each SLB’s influent chemical concentrations in PHREEQC geochemical analyses to verify effluent concentrations and calcite precipitation. Results showed good agreement between the modeled effluent concentrations and the actual data, indicating that this approach can be used to estimate calcite precipitation within SLB systems.

Assessment of percolation through a solid leach bed in dry batch anaerobic digestion processes

This work aimed at assessing water percolation through a solid cow manure leach bed in dry batch AD processes. A laboratory-scale percolation column and an experimental methodology were set up. Water behaviour was modelled by a double porosity medium approach. An experimental procedure was proposed to determine the main hydrodynamic parameters of the multiphase flow model: the porosity, the permeability and the term for water exchange from macro- to micro-porosity. Micro- and macro-porosity values ranged from 0.42 to 0.70m3m−3 and 0.18 to 0.50m3m−3. Intrinsic permeability values for solid cow manure ranged from 5.55·10−11 to 4.75·10−9m2. The term for water exchange was computed using a 2nd order model. The CFD tool developed was used to simulate successive percolation and drainage operations. These results will be used to design leachate recirculation strategies and predict biogas production in full-scale dry AD batch processes.

Two-Stage Dry Anaerobic Digestion of Beach Cast Seaweed and Its Codigestion with Cow Manure

Two-stage, dry anaerobic codigestion of seaweed and solid cow manure was studied on a laboratory scale. A methane yield of 0.14 L/g VSadded was obtained when digesting solid cow manure in a leach bed process and a methane yield of 0.16 L/g VSadded and 0.11 L/g VSadded was obtained from seaweed and seaweed/solid manure in a two-stage anaerobic process, respectively. The results showed that it was beneficial to operate the second stage methane reactor for the digestion of seaweed, which produced 83% of the methane, while the remainder was produced in the first leach bed reactor. Also, the two-stage system was more stable for the codigestion for seaweed and manure when compared to their separate digestion. In addition, the initial ammonia inhibition observed for manure digestion and the acidification of the leach bed reactor in seaweed digestion were both avoided when the materials were codigested. The seaweed had a higher Cd content of 0.2 mg Cd/kg TS than the manure, 0.04 mg Cd/kg TS, and presents a risk of surpassing limit values set for fertiliser quality of seaweed digestate. Evaluation of the heavy metal content of seaweed or a mixture of seaweed and manure digestate is recommended before farmland application.

The impact of increasing organic loading in two phase digestion of food waste

This paper examines the impact of increasing organic loading in a two phase anaerobic digestion system treating commercial food waste. The first phase is a series of sequentially fed leach bed reactors (LBRs). The second phase is an upflow anaerobic sludge bed (UASB). Leachate from the leach beds, form the influent to the UASB. Effluent from the UASB is re-circulated over the leach beds. Flow rates corresponded to 1 volume of leachate per effective LBR volume per day. The theoretical organic loading rate (OLR) of the UASB is based on the conversion of volatile solids (VS) in the LBR to chemical oxygen demand (COD). The experiment was set up such that the theoretical OLR would rise from 7.1 to 8.8 to 11.8kgCODm−3day−1.The system operated effectively at the lowest organic loading rate producing 384LCH4kgVS−1 which corresponded to 72% of the value obtained in a BMP test. COD conversion efficiency was recorded at 75%. The accumulation of COD over the life of the experiment led to a situation whereby the volumetric OLR (product of COD concentration in the leachate by the flow rate) was over twice the theoretical OLR at the end of the experiment (24.3kgVSm−3day−1 versus 11.8kgVSm−3day−1). At the highest loading rate total ammonia nitrogen (TAN) reached levels of 4500mgL−1 with pH levels of 8.15. This resulted in significant reduction of methane production.

Co-fermentation of oil palm lignocellulosic residue with pig manure in anaerobic leach bed reactor for fatty acid production

Batch experiments were performed to investigate the co-fermentation of palm oil empty fruit bunch (EFB) and pig manure (PM) at various PM mixing ratios (%PM) and flushing intervals (FI) over 60-day fermentation time (FT) using anaerobic leach bed reactors. Addition of PM promoted hydrolysis yield (ηh) and acidification yield (ηa) due to the more degradable and soluble nature of PM that gave out organic acids, and nutrients it supplemented. The highest ηh and ηa found were 27.9±0.3% and 51.7±2.6%, respectively. Longer FI that delayed bed flushing prolonged the dry condition where hydrolytic reaction could be enhanced. The developed multiple regression model with R2=0.87 and p<0.0001 suggested a good fit to the data and able to describe the interactive relationship of the parameters on total volatile fatty acids (VFA) production. The longer chain acids, i.e. propionic (C3), butyric (C4), and valeric (C5) acids, were found in higher concentrations with longer FI and higher pig manure mixing ratios. The mixing of an easier biodegradable pig manure as co-substrate could help induce higher degree of fermentation of the recalcitrant EFB.

Microbial community distribution and extracellular enzyme activities in leach bed reactor treating food waste: Effect of different leachate recirculation practices

This study aimed at understanding the relationship between microbial community and extracellular enzyme activities of leach bed reactor (LBR) treating food waste under different leachate recirculation practices (once per day and continuous) and liquid to solid (L/S) ratios (1:1 and 0.5:1). Microbial community analysis using PCR-DGGE revealed that Lactobacillus sp., Bifidobacter sp., and Proteobacteria were the most abundant species. Number of phylotypes was higher in LBRs with intermittent recirculation; whereas, lower number of phylotypes dominated by the key players of degradation was observed with continuous recirculation. The L/S ratio of 1:1 significantly enhanced the volatile solids removal compared with 0.5:1; however, this effect was insignificant under once a day leachate recirculation. Continuous leachate recirculation with 1:1 L/S ratio significantly improved the organic leaching (240gCOD/kgvolatile solid) and showed distinct extracellular enzyme activities suitable for food waste acidogenesis.

Responses of microbial community and acidogenic intermediates to different water regimes in a hybrid solid anaerobic digestion system treating food waste

This study investigated the effects of different water regimes in an acidogenic leach bed reactor (LBR) during 16-day batch mode food waste digestion. LBRs were operated under five water replacement ratios (WRRs) (100%, 75%, 50%, 25% and 5% in LBRs R1, R2, R3, R4 and R5, respectively) and methanogenic effluent (ME) addition with two leachate recirculation frequencies (once in 24h and 12h in LBRs R6 and R7, respectively). Results showed that 50–100% WRRs accelerated the hydrolysis and acidogenesis with butyrate as the dominant product (∼35% of COD); whereas 5–25% WRRs promoted propionate production. The ME recirculation enhanced protein decomposition and reduced ethanol production. Lactobacillus dominated in LBRs with water addition (R1–R5), while Clostridium and hetero-fermenting lactic acid bacteria dominated in LBR with ME addition (R7). The highest volatile solid degradation (82.9%) and methane yield (0.29L-CH4/g VS) were obtained with ME addition at 0.7d hydraulic retention time.