Compost Bioreactors Research Articles

Depuration of landfill leachates using fly ash as a catalyst in solar advanced oxidation processes and a compost bioreactor

Fly ash (FA) is a problematic solid waste coming, for instance, from coal combustion. Herein, FA is used in a solar photocatalytic system to deal with landfill leachates (LL), which is another challenging waste. The photocatalytic process is combined with coagulation-flocculation pretreatment and a compost-based biological post-treatment. FA was characterized initially, showing silicon dioxide (52.25%), aluminum oxide (36.99%), calcium oxide (6.92%), iron oxide (2.47%), and titanium dioxide (1.74%), as the main composing oxides. Also, FA had a low surface area (0.48 m2/g), and high thermal stability (<2% of weight loss at 1000 °C). At the same time, the characterization of LL indicated this is a very polluted liquid, due to its high content of chemical oxygen demand (COD, 8072 mg/L), humic acids (HA, 7320 absorbance at 254 nm), iron (3.1 mg/L), copper (258 mg/L), and a slightly basic pH (8.5). After the coagulation-flocculation pretreatment, the supernatant liquid was submitted to the photocatalytic process (FA/H2O2/sunlight), which removed ∼70% of COD. For the photocatalytic system, the effects of pH, H2O2 concentration, and FA dose were assessed; evidencing that the pH change from 3.0 to 6.0 affected the COD and HA removals strongly. Under proper operating conditions (i.e., FA: 2.0 g/L, H2O2: 2000 mg/L, and pH: 3.0), the photocatalytic process significantly decreased the sample toxicity (∼56%). Thereby, the resultant sample from the FA/H2O2/sunlight system was submitted (for 10 days) to the action of the compost-based biotreatment, comparing the use of non-adapted and adapted aerobic microorganisms. The adapted microorganisms exhibited a higher action, achieving removals of ∼68% and ∼9% for the metals (Fe and Cu) and COD, respectively. The results of this research work demonstrated the good suitability of FA-photocatalysis combined with a coagulation-flocculation pre-treatment and a compost-based biological post-treatment to face problematic landfill leachates.

Use of propionic acid additions to enhance zinc removal from mine drainage in short residence time, flow-through sulfate-reducing bioreactors

The effectiveness of liquid carbon additions to enhance zinc removal in laboratory-scale short hydraulic residence time (19 h) compost bioreactors receiving synthetic mine water with a high influent zinc concentration (45 mg/L) was investigated. Effective removal of such elevated zinc concentrations could not be sustained by sulfate reduction and/or other attenuation processes without carbon supplementation. Propionic acid addition resulted in improved and sustained performance by promoting the activities of sulfate reducing bacteria, leading to efficient zinc removal (mean 99%) via bacterial sulfate reduction. In contrast, cessation of propionic acid addition led to carbon limitation and the growth of sulfur oxidising bacteria, compromising zinc removal by bacterial sulfate reduction. These research findings demonstrate the potential for modest liquid carbon additions to compost-based passive treatment systems to engineer microbial responses which enhance rates of zinc attenuation in a short hydraulic residence time, enabling remediation of highly polluting mine drainage at sites with limited land availability.

Heat Recovery of Compost Reactors: Field Study of Operational Behaviour, Heating Power and Influence Factors

Abstract This study evaluates the common process and set-up design of a static compost bioreactor for heat recovery. A technology, which fits the goal of a sustainable, growing bioeconomy which combines the utilization of compost heat and compost material. Interest on this technology has been growing the last years but precise data of pilot scale reactors is rare. Data is required to adjust the process for custom needs and further technical development. Therefore, lignin-cellulose based biomass was composted in unaerated cylindrical compost reactors size 20 to 70 m3 for 140 days. The biomass comes with C:N ratio of about 25:1, water content of 43-48 %, organic matter content of 40.6 % d.m. and calorific value of 8.3 MJ/kg d.m. Spatial distribution of temperature and gas concentration (oxygen, carbon dioxide, methane) within the reactor shows methane production of the anaerobic core area. Maximum thermal power of 5.2 kW from a 63 m3 reactor with average temperature of heating flow about 40 °C was reached. Maximum recovered heating power of 4.8 MJ/kg d.m. was calculated for an operation of 6 month. This corresponds to 50 % of the measured calorific value. Biggest influence factors detected on the recovered heating power of the pilot scale reactor has been the size of reactor, the set up quality and the control of heat exchanger. The spatial correlation between heat production and aerobic digestion suggests a technical development in terms of aeration.

Untapped potential of zeolites in optimization of food waste composting

This study aims to examine the effect of zeolites in optimizing the process of food waste composting. A novel method of sequential hydrothermal was introduced to modify the natural zeolite and apply to in-vessel compost bioreactors. Raw and modified natural zeolites were applied at 10 and 15% (w/w) of the total waste and compared with un-amended control trial. Both raw and modified zeolites affected the composting process, but the notable results were observed for modified natural zeolite. The results for compost stability parameters were prominent at 15% modified natural zeolite concentration. The rapid and long-term thermophillic temperature and moisture content reduction to the optimum range was observed for modified natural zeolite. Furthermore, the total ammonium (NH4+) and nitrate (NO3−) concentration in modified natural zeolite were increased by 11.1 and 21.5% respectively as compared to raw zeolite. Compost stability against moisture contents (MC), electrical conductivity (EC), organic matters (OM), total carbon (TC), mineral nitrogen, nitrification index (NI) and germination index (GI) was achieved after 60 days of composting that was in accordance with the international compost quality standards. The findings of this study suggested the suitability of modified natural zeolite addition at 15% to the total waste as the optimum ratio for the composting of food waste in order to achieve a stable nutrient-rich compost.

Design and Performance of Helical Ribbon and Screw Impeller Aerobic Compost Bioreactor

In order to solve problems of raw materials present in the compost reactor are compacted blocks, poor ventilation performance, large ventilation resistance, and difficulty in homogenizing the product, a helical ribbon and screw impeller aerobic compost bioreactor was developed. Through numerical simulation of the flow field, it is proved that the helical ribbon and screw impeller has a good agitation and axial flow property. The results of the composting test show that the time above 55°C for the top, middle, and bottom layers is 5.2, 4.7, and 4.3 days. During the reaction, the oxygen concentration was over 8%, and the final seed germination index of each layer was over 88%, which proved that the experimental reactor can achieve homogenization and can be effectively harmless compost.

Optimization of food waste compost with the use of biochar

This paper aims to examine the influence of biochar produced from lawn waste in accelerating the degradation and mineralization rates of food waste compost. Biochar produced at two different temperatures (350 and 450 °C) was applied at the rates 10 and 15% (w/w) of the total waste to an in-vessel compost bioreactor for evaluating its effects on food waste compost. The quality of compost was assessed against stabilization indices such as moisture contents (MC), electrical conductivity (EC), organic matters (OM) degradation, change in total carbon (TC) and mineral nitrogen contents such as ammonium (NH4+) and nitrate (NO3−). The use of biochar significantly improved the composting process and physiochemical properties of the final compost. Results showed that in comparison to control trial, biochar amended compost mixtures rapidly achieved the thermophilic temperature, increased the OM degradation by 14.4–15.3%, concentration of NH4+ by 37.8–45.6% and NO3− by 50–62%. The most prominent effects in term of achieving rapid thermophilic temperature and a higher concentration of NH4+ and NO3− were observed at 15% (w/w) biochar. According to compost quality standard of United States (US), California, Germany, and Austria, the compost stability as a result of biochar addition was achieved in 50–60 days. Nonetheless, the biochar produced at 450 °C had similar effects as to biochar produced at 350 °C for most of the compost parameters. Therefore, it is recommended to produce biochar at 350 °C to reduce the energy requirements for resource recovery of biomass and should be added at a concentration of 15% (w/w) to the compost bioreactor for achieving a stable compost.

Applicability of passive compost bioreactors for treatment of extremely acidic and saline waters in semi-arid climates

Extremely acidic and saline groundwater occurs naturally in south-western Australia. Discharge of this water to surface waters has increased following extensive clearing of native vegetation for agriculture and is likely to have negative environmental impacts. The use of passive treatment systems to manage the acidic discharge and its impacts is complicated by the region's semi-arid climate with hot dry summers and resulting periods of no flow. This study evaluates the performance of a pilot-scale compost bioreactor treating extremely acidic and saline drainage under semi-arid climatic conditions over a period of 2.5 years. The bioreactor's substrate consisted of municipal waste organics (MWO) mixed with 10 wt% recycled limestone. After the start-up phase the compost bioreactor raised the pH from ≤3.7 to ≥7 and produced net alkaline outflow for 126 days. The bioreactor removed up to 28 g/m2/d CaCO3 equivalent of acidity and acidity removal was found to be load dependent during the first and third year. Extended drying over summer combined with high salinity caused the formation of a salt-clay surface layer on top of the substrate, which was both beneficial and detrimental for bioreactor performance. The surface layer prevented the dehydration of the substrate and ensured it remained waterlogged when the water level in the bioreactor fell below the substrate surface in summer. However, when flow resumed the salt-clay layer acted as a barrier between the water and substrate decreasing performance efficiency. Performance increased again when the surface layer was broken up indicating that the negative climatic impacts can be managed. Based on substrate analysis after 1.5 years of operation, limestone dissolution was found to be the dominant acidity removal process contributing up to 78–91% of alkalinity generation, while bacterial sulfate reduction produced at least 9–22% of the total alkalinity. The substrate might last up to five years before the limestone is exhausted and would need to be replenished. The MWO substrate was found to release metals (Zn, Cu, Pb, Ni and Cr) and cannot be recommended for use in passive treatment systems unless the risk of metal release is addressed.

The Influence of Engineering Scale and Environmental Conditions on the Performance of Compost Bioreactors for the Remediation of Zinc in Mine Water Discharges

The effects of engineering scale on the performance of a compost-based system for the remediation of a discharge from an abandoned metal mine was investigated by simultaneous operation, under field conditions, of a laboratory-scale column and a pilot-scale system. The two systems contained identical reactive substrate, comprising limestone gravel, compost, wood chips and activated sludge from a municipal waste water treatment plant, and had an initial hydraulic residence time of approximately 19 h. The influent mine water contained around 2–2.5 mg/L zinc and had a circumneutral pH. Clear differences in the performance of the systems were seen, demonstrating the importance of engineering scale in the remediation of zinc. The laboratory-scale column was most effective at removing zinc, with approximately 96 % of the influent zinc attenuated within the system, while the pilot scale system removed, on average, 84 % of the influent zinc. The poorer performance of the pilot-scale reactor may, in part, be due to preferential flow, as indicated by a greater reduction in hydraulic residence time than in the laboratory-scale system. Early indications are that temperature also plays an important role in the attenuation of zinc within such systems, possibly linked to reduced microbial activity during periods of low temperature. Despite an apparent decrease in sulphate concentration within both systems, it is unclear whether bacterial sulphate reduction is the dominant mechanism for metal removal or whether sorption processes prevail. Implications for full-scale design of these treatment systems are discussed.

Degradation of Polyethylene Film Samples Containing Oxo-Degradable Additives

The introduction of the so called oxo-biodegradable additives in the Argentine market motivated the assessment of the effects of abiotic and biotic factors on the structure and mechanical behavior of polyethylene (PE) with oxo-degradable additives (PE+AD). Samples of oxo-degradable packaging films found in local shops together with polyethylene films with and without d2ẅ additive were annealed at different temperatures between 50 and 110¼C and submitted to ultraviolet radiation at different irradiances (0,35; 0,45; 0,89 and 1,20W/m2). Furthermore, aged oxo-degradable films were set in a controlled compost bioreactor in order to evaluate their biodegradation ability. Experimental results showed that elongation at break was the mechanical property more sensitive to the polymeric degradation. The structural changes determined by FT-IR remarked the importance of the UV degradation time over the irradiation rate; the carbonyl index of the degraded samples pointed out that chain scission was a thermally activated process. Regarding degradation due to UV radiation, at the same dose, the elongation at break is lower at lower irradiance both in PE and PE+AD samples. On the other hand, thermal degradation of PE without additive is more susceptible to degradation than PE + AD. At the beginning of the biodegradation tests, PE + AD showed a higher CO2 production rate with respect to PE; however, this rate reduced along the first 30 days, reaching the CO2 production of PE without additive. The maximum biodegradation observed for both PE and PE+AD samples was 24% after 90 days of incubation.

Heavy metals removal from mine runoff using compost bioreactors

Permeable bioreactors have gained both research and management attention as viable methods for treating mine runoff waters. We examined the operation of a field‐scale bioreactor (containing mixed compost, straw and gravel) for treatment of runoff from the Mother Load (ML) mine in northern Idaho, U.S. and compared it to an experimental laboratory‐scale reactor, containing a similar matrix and treating similar mine runoff water. In general both reactors were efficient in removing most of the metals assayed, Al, As, Cd, Fe, Ni, Pb and Zn, with the exception of Mn. Both systems showed evidence of bacterial‐mediated sulphate reduction and concomitant metal sulphide complexes. However, the experimental laboratory bioreactor showed greater proportions of immobile metals reductions than did the ML bioreactor, presumably due to the greater action of sulphate‐reducing bacteria. The major metal removal mechanism in the ML bioreactor was surmised to be adsorption. Differences in metal removal mechanisms between the reactors were hypothesized to be due to fluctuating hydraulic residence times at the ML site, in turn, due to unregulated runoff flow.

Enzyme activity as affected by surfactant APG in dairy manure compost in bioreactor

利用堆肥反应器严格控制堆肥条件, 以牛粪为主要原料进行好氧堆肥, 在堆肥过程中加入表面活性剂烷基多糖苷(APG), 研究其对堆肥中微生物数量以及酶活性变化的影响。结果表明: 在好氧堆肥中添加表面活性剂APG对堆肥中的微生物无显著抑制作用, 微生物数量无显著变化(<i>P</i>>0.05); 但可以促进堆肥升温, 延长高温期。加入APG对堆肥中的过氧化氢酶活性几乎无影响, 最终APG处理和CK处理的酶活性值均达到1.17 mmol·g^-1左右; 加入APG后脲酶活性略有提高, 第2 d APG处理和CK处理的脲酶活性均达到峰值, 分别为32.15 mg(NH₃-N)·g^-1·24h^-1和30.17 mg(NH₃-N)·g^-1·24h^-1, 差异不显著(P>0.05), 第7 d达到最低值, 分别为0.81 mg(NH₃-N)·g^-1·24h^-1和0.38 mg(NH₃-N)·g^-1·24h^-1, 差异显著(P<0.05); APG处理对转化酶和纤维素酶活性均有明显的提高作用, 其中转化酶在第3 d加APG处理和CK处理峰值分别为18.15 mg(葡萄糖)·g^-1·24h^-1和11.77 mg(葡萄糖)·g^-1·24h^-1, 第21 d两处理峰值分别为24.09 mg(葡萄糖)·g^-1·24h^-1和20.71 mg(葡萄糖)·g^-1·24h^-1, 差异显著(P<0.05); 纤维素酶在第3 d加APG处理和CK处理峰值分别为58.77 mg·min^-1和30.62 mg·min^-1, 差异显著(<i>P</i><0.05)。本试验结果表明, 添加表面活性剂APG可以提高堆肥中转化酶和纤维素酶活性, 促进堆肥中有机物质的转化, 一定程度上加快好氧堆肥进程。

Increasing nitrogen conservation by adding urease inhibitor NBPT to chicken compost manure

利用堆肥反应器, 以鸡粪和蘑菇渣为原料进行好氧堆肥, 在堆肥中添加不同浓度的脲酶抑制剂NBPT, 研究其对堆肥氮素转化的影响及保氮效果。结果表明: 添加不同浓度的脲酶抑制剂NBPT对堆肥进程中温度无显著影响, 在堆肥的高温阶段可有效控制堆料pH的升高, 在堆肥高温前期的0~10 d可有效降低堆肥的脲酶活性, 在堆肥中后期10~25 d明显提高全氮含量。堆肥25 d后, 添加0.04 mL·kg^-1、0.08 mL·kg^-1、0.16 mL·kg^-1脲酶抑制剂NBPT分别比CK减少氮素损失6.61%、4.89%和13.51%。堆肥过程中, 堆料铵态氮含量呈升-降-升-降的双峰趋势, 且大部分时间CK处理的铵态氮含量高于添加脲酶抑制剂NBPT处理, 且CK处理铵态氮的两次升高速度均高于添加脲酶抑制剂NBPT处理。在堆肥的升温和高温期硝态氮含量不稳定, 但堆肥结束时, 各添加脲酶抑制剂NBPT处理的硝态氮含量显著高于CK处理。本试验结果表明, 在堆肥过程中添加脲酶抑制剂NBPT可延缓鸡粪中的尿素态氮向铵态氮的转化, 增加堆肥成品中的硝态氮含量。在畜禽粪好氧堆肥中加入脲酶抑制NBPT可起到一定的保氮作用。

Pathogen Inactivation In Cow Manure Compost

During aerobic composting of animal manure, microbial activity within the mixture generates heat and metabolic by-products that inactivate zoonotic pathogens. Although it is recognized that the type and level of microbial activity will vary with the nutrient availability of different compost ingredients, the degree to which these changes could impact pathogen inactivation is of interest. Towards that goal, the purpose of this study was to determine inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in compost laboratory-scale bioreactor systems formulated to different initial carbon:nitrogen (C:N) ratios with cow manure, straw, and cottonseed meal. The C:N ratio did not significantly affect the time to inactivation of Listeria monocytogenes. In contrast, Escherichia coli O157:H7 survived for significantly (P < 0.05) longer periods of time in 40:1 C:N systems than in 30:1 or 20:1 systems even though the cumulative heat exposures were statistically similar in the systems. An increase of pH values to 8 to 9 occurred initially for 40:1 C:N systems, whereas the pH of the 20:1 and 30:1 systems initially declined to 5.5 to 6 before increasing to 8 to 9 after 2 days of composting.

Microbiology of a wetland ecosystem constructed to remediate mine drainage from a heavy metal mine

A pilot passive treatment plant (PPTP) was constructed to evaluate the potential of a composite wetland system to remediate acidic, metal-rich water draining the former Wheal Jane tin, in Cornwall, England. The treatment plant consists of three separate and controllable composite systems, each of which comprises a series of aerobic wetlands for iron oxidation and precipitation, a compost bioreactor for removing chalcophilic metals and to generate alkalinity, and rock filter ponds for removing soluble manganese and organic carbon. To understand the roles of microorganisms in remediating acid mine drainage (AMD) in constructed wetland ecosystems, populations of different groups of cultivatable acidophilic microbes in the various components of the Wheal Jane PPTP were enumerated over a 30-month period. Initially, moderately acidophilic iron-oxidising bacteria (related to Halothiobacillus neapolitanus) were found to be the major cultivatable microorganisms present in the untreated AMD, though later heterotrophic acidophiles emerged as the dominant group, on a numerical basis. Culturable microbes in the surface waters and sediments of the aerobic wetlands were similarly dominated by heterotrophic acidophiles, though both moderately and extremely acidophilic iron-oxidising bacteria were also present in significant numbers. The dominant microbial isolate in waters draining the anaerobic compost bioreactors was an iron- and sulfur-oxidising moderate acidophile that was closely related to Thiomonas intermedia. The acidophiles enumerated at the Wheal Jane PPTP accounted for 1% to 25% of the total microbial population. Phylogenetic analysis of 14 isolates from various components of the Wheal Jane PPTP showed that, whilst many of these bacteria were commonly encountered acidophiles, some of these had not been previously encountered in AMD and AMD-impacted environments.

Biogeochemistry of the compost bioreactor components of a composite acid mine drainage passive remediation system

The compost bioreactor (“anaerobic cell”) components of three composite passive remediation systems constructed to treat acid mine drainage (AMD) at the former Wheal Jane tin mine, Cornwall, UK were studied over a period of 16 months. While there was some amelioration of the preprocessed AMD in each of the three compost bioreactors, as evidenced by pH increase and decrease in metal concentrations, only one of the cells showed effective removal of the two dominant heavy metals (iron and zinc) present. With two of the compost bioreactors, concentrations of soluble (ferrous) iron draining the cells were significantly greater than those entering the reactors, indicating that there was net mobilisation (by reductive dissolution) of colloidal and/or solid-phase ferric iron compounds within the cells. Soluble sulfide was also detected in waters draining all three compost bioreactors which was rapidly oxidised, in contrast to ferrous iron. Oxidation and hydrolysis of iron, together with sulfide oxidation, resulted in reacidification of processed AMD downstream of the compost bioreactors in two of the passive treatment systems. The dominant cultivatable microorganism in waters draining the compost bioreactors was identified, via analysis of its 16S rRNA gene, as a Thiomonas sp. and was capable of accelerating the dissimilatory oxidation of both ferrous iron and reduced sulfur compounds. Sulfate-reducing bacteria (SRB) were also detected, although only in the bioreactor that was performing well were these present in significant numbers. This particular compost bioreactor had been shut down for 10 months prior to the monitoring period due to operational problems. This unforeseen event appears to have allowed more successful development of AMD-tolerant and other microbial populations with critical roles in AMD bioremediation, including neutrophilic SRB (nSRB), in this compost bioreactor than in the other two, where the throughput of AMD was not interrupted. This study has revealed new insights into the operation of compost bioreactors used to remediate mine waters and has shown that, when operated under appropriate conditions, they can be highly efficient at generating alkalinity and removing metals from extremely acidic, metal-rich AMD.

Biological manganese removal from acid mine drainage in constructed wetlands and prototype bioreactors

Mine drainage waters vary considerably in the range and concentration of heavy metals they contain. Besides iron, manganese is frequently present at elevated concentrations in waters draining both coal and metal mines. Passive treatment systems (aerobic wetlands and compost bioreactors) are designed to remove iron by biologically induced oxidation/precipitation. Manganese, however, is problematic as it does not readily form sulfidic minerals and requires elevated pH (>8) for abiotic oxidation of Mn (II) to insoluble Mn (IV). As a result, manganese removal in passive remediation systems is often less effective than removal of iron. This was found to be the case at the pilot passive treatment plant (PPTP) constructed to treat water draining the former Wheal Jane tin mine in Cornwall, UK, where effective removal of manganese occurred only in one of the three rock filter components of the composite systems over a 1-year period of monitoring. Water in the two rock filter systems where manganese removal was relatively poor was generally <pH 5, whereas it was significantly higher (∼pH 7) in the third (effective) system. These differences in water chemistry and manganese removal were due to variable performances in the compost bioreactors that feed the rock filter units in the composite passive systems at Wheal Jane. An alternative approach for removing soluble manganese from mine waters, using fixed bed bioreactors, was developed. Ferromanganese nodules (about 2 cm diameter), collected from an abandoned mine adit in north Wales, were used to inoculate the bioreactors (working volume ca. 700 ml). Following colonization by manganese-oxidizing microbes, the aerated bioreactor catalysed the removal of soluble manganese, via oxidation of Mn (II) and precipitation of the resultant Mn (IV) in the bioreactor, in synthetic media and mine water from the Wheal Jane PPTP. Such an approach has potential application for removing soluble Mn from mine streams and other Mn-contaminated water courses.

Remediation of Petroleum Impacted Soils in Fungal Compost Bioreactors

The ability of the white rot fungus Phanerochaete chrysosporium to enhance the biotransformation of benzo(a)pyrene (B(a)P) in contaminated soils was evaluated in compost bioreactors. Radiolabelled114C and chemical mass balances were used to evaluate: 1) rate of disappearance of test compound; 2) mineralization; 3) formation of bound contaminant residue; and 4) treatment costs. Mineralization of B(a)P was found to be insignificant over the duration of test period. Moreover, no radioactivity was recovered in volatile organic traps indicating that transformation of B(a)P resulted in chemicals intermediates that remained associated with the compost matrix. Bound contaminant residue formation was found to be the major mechanism of B(a)P removal accounting for nearly 100% of the contaminant loss from the solvent extract (methylene chloride/acetone). A maximum rate of bound contaminant removal of 1.36 mg B(a)P/Kg soil-day was estimated in fungal inoculated system over the first thirty days of treatment. This was significantly different from the maximum rate of bound residue formation estimated in the noninoculated systems (0.83 mg B(a)P/Kg soil-day) over the same time period. After thirty days, the rate of bound residue formation decreased to near zero in the inoculated system while remaining constant in the noninoculated reactors. The decrease in bound residue formation coincided with decline in benzo(a)pyrene removal. Data suggest that fungal activity may have been reduced over time by nutrient limitation.