Types Of Anaerobic Digesters Research Articles

Modelling of Amino Acid Fermentations and Stabilization of Anaerobic Digestates by Extracting Ammonium Bicarbonate

With the current increase in demand for animal and agricultural products, management of agrowaste has become critical to avoid greenhouse gas emissions. The present article investigates the applicability of ammonium bicarbonate synthesis via flash distillation to valorize and stabilize several types of anaerobic digestates which are produced from individual fermentations of amino acids. The content of CO2 in the digestate was found to be responsible for the OH alkalinity (0.4 equivalents of acid/kg digestate), while the partial and total alkalinities (0.8 eq/kg digestate) were essentially derived from the content of NH3. The most suitable conditions for the flash distillation were 95 °C and 1 bar with the condensation occurring at 25 °C. However, in order to attain the precipitation of NH4HCO3 in the distillate, it was necessary to consider digestates with a moisture content of 50 wt.%, since saturation levels of inorganic nitrogen and inorganic carbon were not attained otherwise. Even under these conditions, few amino acids (i.e., arginine, glycine, and histidine) were able to provide an anaerobic digestate upon fermentation that would be suitable for NH4HCO3 stabilization. The process of stabilization with a capacity of a t of digestate per h was improved by adding hydrochloric acid or sodium hydroxide at a rate of 44 kg/h, leading to production of 34 kg NH4HCO3/h. Given the role of the volatile elements of the biogas as endogenous stripping agents, it is recommended to use a fresh and saturated digestate as feed for the flash distillation.

Iron-Based Additives and Biogas Production from Organic Wastes Using Anaerobic Digestion Process

The world is facing a serious energy crisis and environmental pollution problems due to a sharp increase in the world population. Bioenergy is an eminent solution to these problems. Anaerobic digestion is a green energy technology used worldwide for the conversion of organic waste to biogas. It is reported that organic wastes are hard to digest and need some technical improvement in the anaerobic digestion process to improve biogas yield. Iron-based additives, due to their electron acceptance and donation capabilities, have been emphasized as being exceptional in improving anaerobic digestion process efficiency amongst all other enhancement options. This study reviews the major available types of iron-based additives, their characteristics, and their preparation methods. The preferred iron-based additive that has a significant effect on the enhancement of biogas yield is also discussed. The use of iron-based additives in the anaerobic digestion process with varying dosages and their impact on the biogas generation rate is also being studied. Substrates, operating parameters, and types of anaerobic digesters used in recent studies while researching the effects of iron-based additives are also part of this review. Lastly, this study also confirms that iron-based additives have a significant effect on the reduction rate of the volatile suspended solids, methane content, biogas yield, and volatile fatty acids.

Monitoring N : P Ratio and Cd, Cu, Pb, and Zn Contents in Different Types of Anaerobic Digestates: A Six-Year Study Case

Depending on the quality of the input substrates, process parameters, and postfermentation treatments, digestates may contain a broad spectrum of potentially toxic elements. We suspected that these contents may vary on a broad scale even under seemingly stable process conditions at the biogas plant. Digestates from four biogas plants were therefore continuously analyzed for their contents of phosphorus, nitrogen, cadmium, copper, lead, and zinc over a period of six years. The input substrates varied between the plants (e.g., cattle and pig slurry and rye and maize silage), but were the same for each plant over the whole period. The N : P ratio of the digestates ranged from 2 to 24, with the digestate coming from cofermentation of pig slurry and energy crops (“DG Pig”) having the widest range of N : P ratio over the years. Heavy metal loads of all digestates and during all evaluations did not exceed the limits set by European or German legislation, but as previously expected, showed a large variability especially if cattle or pig manure were used as substrates. Copper content of Cattle slurry before digestion was 897.7 mg kg−1 DM in one case, and zinc content of DG Pig reached 590.2 mg kg−1 DM also once during the investigation. As a result, we strongly recommend to monitor especially phosphorus, copper, and zinc contents in digestates very closely and in short intervals.

Biofertilisation with Anaerobic Digestates: Effects on the Productive Traits of Ryegrass and Soil Nutrients

This study investigated how repeated applications of different types of anaerobic digestates and undigested cattle slurry affected the growth responses and nutritional aspects of ryegrass swards (Lolium perenne L.) and soil nutrient concentrations, in a two-season field trial. The treatments included four different types of anaerobic digestate, undigested cattle slurry, nitrogen control (N-control) with calcium ammonium nitrate (CAN) and a no fertiliser control, distributed in a randomised block design with three replicates. The different types of biofertilisers drove a comparable average forage daily growth rate varying between 65 and 79 kg ha???1 day???1 (p???>???0.05). Crude protein and neutral or acid detergent fibre of the forage were not influenced by any type of biofertiliser (p???>???0.05). Most of the anaerobic digestates led to increases in the level of soil available P and K (p???<???0.05). Despite the detectable influence of the levels of NPK in the biofertilisers on the plant growth responses, different anaerobic digestates when applied using the same dry matter amounts can drive comparable forage grass growth responses with low influence over the nutritional quality of the ryegrass forage. Repeated applications of anaerobic digestates can help to increase or reduce the losses of the soil available P and K. The application of anaerobic digestate, cattle slurry and calcium ammonium nitrate led to increases in the N content of the soil; however, there were no differences between them, despite their considerable differences in terms of N inputs. This might be linked to the volatility and losses of the readily available N from the biofertilisers applied.

Determination of microbial numbers in anaerobically digested biofertilisers

ABSTRACT This study aimed to quantity total numbers of bacteria, fungi and archaea in different types of commercial liquid anaerobic digestates, and to identify common patterns in their microbial numbers post-digestion and possible implications of their use as biofertiliser. Relationships between microbial numbers and physical–chemical traits of the digestates were also investigated. Quantification was performed using culturable and molecular (quantitative PCR) approaches. Bacterial and fungal CFUs ranged up to five orders of magnitude (105–1010; 0–105 g−1 DW, respectively) between different types of anaerobic digestates. Bacterial, archaeal and fungal gene copy numbers (GCN) varied by two orders of magnitude (108–1010; 107–109; 104–106 g−1 DW, respectively) between digestates. All microbial variables analysed showed significant differences between the different types of anaerobic digestate investigated (p < 0.05). Culturable microbial numbers for fungi (6.43 × 104 CFU g−1 DW) were much lower than for bacteria (2.23 × 109 CFU g−1 DW). Gene copy numbers were highest for bacteria (16S) (1.09 × 1010 g−1 DW), followed by archaea (16S) (5.87 × 108 g−1 DW), and fungi (18S) (1.77 × 106 g−1 DW). Liquid anaerobic digestates were predominantly dominated by bacteria, followed by archaeal and fungal populations. At 50% similarity level, the microbial profiles of the eleven anaerobic digestates tested separated into just two groups, indicating a broad relative degree of similarity in terms of microbial numbers. Higher bacterial (16S) GCN was associated with low OM and C/N ratio in digestates.

Bacterial Succession in the Thermophilic Phase of Composting of Anaerobic Digestates

Organic matter degradation and bacterial communities associated to the thermophilic phase of composting were compared using two different types of anaerobic digestates, one from a sewage sludge digester (SD), and the other from an agricultural digester (AD). The composting process exhibited similar variations in temperature, pH, moisture content and bacterial profiles, despite the inherent feedstock differences along with distinctive initial bacterial composition. According to the data obtained from 16S rRNA gene amplicon sequencing, SD constituted more than 20 bacterial phyla with Proteobacteria (21%) and Chloroflexi (21%) being predominant, meanwhile AD was represented by only 7 phyla in which Firmicutes was the most abundant phylum (73%). Nevertheless, bacterial community profiles of the two composting systems became more similarly represented at the phylum level, both dominated by Proteobacteria (65% in AD and 61% in SD), whereas Chromatiaceae and Sphingomonadaceae were the most abundant families in AD and SD, respectively. Highly diverse but similar bacterial communities were detected during the composting of different anaerobic digestates at the thermophilic phase.

Isolation and characterization of plant growth promoting bacteria (PGPB) from anaerobic digestate and their effect on common wheat (Triticum aestivum) seedling growth

The use of anaerobic digestate as fertilizer is considered beneficial since it provides plant nutrients and organic matter to soils. However, there is limited information about plant growth promoting bacteria (PGPB) in digestate. In this study, we isolated Bacillus and Pseudomonas from two types of anaerobic digestates, and selected three different plant growth promoting traits and antifungal activity to screen 200 bacteria isolated from each digestate. Then 6 isolates based on plant growth promoting traits were selected and inoculated with common wheat seeds to evaluate their plant growth promoting activity. Cultivable population of Bacillus and Pseudomonas were 2.20 × 106 and 6.98 × 104 CFU g-1 dry matter in mesophilic digestate, while were 6.86 × 105 and 5.65 × 104 CFU g-1 dry matter in thermophilic digestate. Twenty-five bacterial isolates from mesophilic digestate and 12 bacterial isolates from thermophilic digestate showed positive plant growth promoting traits or antifungal activity. In plant growth promoting assay, all isolates significantly promoted growth of wheat seedlings (p less than 0.05). Seedlings stem length was increased from 28.5% to 38.6% by bacteria inoculation. In addition, bacteria inoculation increased seedlings stem weight from 113.3% to 214.2% and root weight from 108.6% to 207.2% as compared to un-inoculated control. The results showed that anaerobic digestate was a potential source for isolation of PGPB, and PGPB in digestate would be beneficial for plant growth with fertilizer application.

Production of methane gas from organic fraction municipal solid waste (OFMSW) via anaerobic process: application methodology for the Malaysian condition

Solid waste management in Malaysia is confronted with many problems, including low collection coverage, irregular collection services, inadequate equipment used for waste collection, crude open dumping and burning without air and water pollution control systems, inadequate legal provisions and resource constraints. These problems have various effects on the development of the solid waste management system in Malaysia. Anaerobic digestion has been suggested as an alternative method for removing high concentrations of organic waste. In this study, two types of anaerobic digesters which are Simulated Landfill Bioreactor (SLBR) and Anaerobic Solid-Liquid (ASL) reactor were proposed. The reactors were operated at a temperature 60°C, analysed for biogas production and volatile fatty acid.

Recovery of methane-rich gas from solid-feed anaerobic digestion of ipomoea ( Ipomoea carnea)

Studies are presented on new types of anaerobic digesters in which chopped or dry crushed Ipomoea carnea was fed without any other pretreatment, in an attempt to develop commercially viable means of utilizing the otherwise very harmful plant. Two types of solid-feed anaerobic digesters (SFADs) were studied. The first type had a single vessel in which the bottom 35% portion was separated from the top portion by a perforated PVC disk. The weed was charged from the top and inoculated with anaerobically digested cowdung–water slurry. The fermentation of the weed in the reactor led to the formation of volatile fatty acids (VFAs) plus some biogas. The leachate, rich in the VFAs, was passed through the perforated PVC sheet and collected in the lower portion of the vessel. The other type of reactors had two vessels, the first one was fully charged with the weed and the second received the VFA leachate. With both types were attached upflow anaerobic filters (UAFs) which converted the leachate into combustible biogas consisting of ∼70% methane. All SFADs developed very consistent performance in terms of biogas yield within 17 weeks of start. The two-compartment reactors yielded significantly more biogas than the single-compartment reactors of corresponding total volume, and the reactors with which anaerobic filters (AF) were attached yielded more biogas than the ones without AF. The best performing units generated 2.41 m 3 of biogas per m 3 of digester volume, as compared to 0.1–0.2 m 3 of biogas, m −3 d −1, obtainable with conventional digesters. This indicates the viability of this technology. The spent weed can be vermicomposted directly to obtain good soil-conditioner cum fertilizer; earthworm Eudrilus eugeniae produced 540 mg vermicast per animal every day, achieving near total conversion of feed to vermicast in 20 days. The proposed systems, thus, makes it possible to accomplish total utilization of ipomoea.

Enhanced primary treatment of concentrated black water and kitchen residues within DESAR concept using two types of anaerobic digesters

Anaerobic digestion of concentrated domestic wastewater streams--black or brown water, and solid fraction of kitchen waste is considered as a core technology in a source separation based sanitation concept (DESAR--decentralised sanitation and reuse). A simple anaerobic digester can be implemented for an enhanced primary treatment or, in some situations, as a main treatment. Two reactor configurations were extensively studied; accumulation system (AC) and UASB septic tank at 15, 20 and 25 degrees C. Due to long retention times in an AC reactor, far stabilisation of treated medium can be accomplished with methanisation up to 60%. The AC systems are the most suitable to apply when the volume of waste to be treated is minimal and when a direct reuse of a treated medium in agriculture is possible. Digested effluent contains both liquid and solids. In a UASB septic tank, efficient separation of solids and liquid is accomplished. The total COD removal was above 80% at 25 degrees C. The effluent contains COD and nutrients, mainly in a soluble form. The frequency of excess sludge removal is low and sludge is well stabilised due to a long accumulation time.

Anaerobic digestion of total raw olive-oil wastewater in a two-stage pilot-plant (up-flow and fixed-bed bioreactors)

A study was undertaken to evaluate the anaerobic digestion of total raw olive-oil wastewater in a two-stage pilot-plant with reactors connected in series. Two different types of anaerobic digesters were used, an up-flow type and a fixed-bed type. The main pupose of the study was to evaluate the performance of an up-flow-type reactor working in series with a fixed-bed-type reactor, which was used as a complementary treatment. The pilot-plant system operated in the mesophilic range (35 ± 1°C) during approximately 390 days, and with organic loading levels that ranged between 2.8 and 12.7 g COD/l.day. Concentrated aqueous ammonia was added to the total raw wastewater to adjust the C/N ratio to the optimum value of 20/1, and this also achieved stabilisation of the pH values in the digesters within a range about neutrality. In a series of seven consecutive experiments, for the first stage (up-flow digester) optimum values of specific biogas production rate stabilised at a value of 2.1 litres/litre digester.day with a very satisfactory COD reduction of 83% (with a volumetric load of 11 g COD/l.day). For the second stage (fixed-bed digester), the biogas production rate stabilised at a value of 0.22 litres/litre digester.day with a COD reduction of 8% (with a volumetric load of 0.19 g COD/l.d). According to the results reported in the literature for total raw wastewater, the performance of the applied system is amongst the best for biogas production, COD reduction and loading rate reported so far, especially for the up-flow digester. Phenols were greatly reduced during the anaerobic digestion process in both digesters, with a concentration reduction which reached 75% in the up-flow digester; with the use of the second stage (fixed-bed reactor) a further reduction of 45% was obtained. With the above encouraging results we may suggest the employment of the up-flow type digester as an economical and effective treatment for significantly reducing the organic load of total raw wastewater. More satisfactory results might be expected from the use of a fixed-bed-type digester connected in series with a previous one, as a second treatment stage.

Performance of four types of anaerobic reactors in treating very dilute dairy wastewater

Anaerobic digestion is a key process in the integrated three-stage system widely adopted for treating wastewater from livestock production in Taiwan. The red mud plastic (RMP) digester is the most common digester used. It is a modified baffled reactor. The current design recommendation for this digester is based on a 10 days hydraulic retention time (HRT). This seems an over-design for dairy wastewater, since such wastewater is often very dilute due to large volumes of cleaning water used. This study reports on the performances of four types of anaerobic digesters (CSTR, UASB, UAF and baffled) treating very dilute dairy wastewater. Experiments were conducted with HRTs between 18.8 and 2 days and with organic loading rates between 0.117 and 1.303 g VS l −1 day −1. Establishment of methanogenesis seems slower for the CSTR and the baffled reactors. The baffled reactors could achieve a solids retention time (SRT) of 31 days when its HRT was 4 days. Effluent SS and COD from the UASB, the UAF and the baffled reactors operated at HRTs of 5, 4 and 3 days met discharge standards. The baffled reactor is preferred for its operational simplicity. The results indicated that for very dilute dairy wastewater, the design HRT of a baffled reactor could be shortened to less than 5 days.

Controlled anaerobic digestion of settled olive-oil wastewater

Abstract A study was undertaken to investigate controlled mesophilic anaerobic digestion of both the supernatant and the sludge from settled olive-oil wastewater. Two different types of anaerobic digesters were used, a fixed-bed type for the supernatant and a plug-flow type for the sludge. Concentrated aqueous ammonia and sodium carbonate were added to adjust the C/N ratio and the pH of the solution in each digester. In both digesters, biogas production and chemical oxygen demand (COD) reduction exceeded the rates mentioned in the literature for diluted raw olive-oil wastewaters. In the digester fed with the supernatant, biogas production rate was stabilised at a mean value of 1·86 litres/litre working volume (average of 24 biogas values) with a COD reduction of 90·91%. In the digester fed with the settled sludge, biogas production rate was stabilised at a mean value of 2·75 litres/litre working volume (average of 12 biogas values) with a COD reduction of 94·95%. These values expressed for the total olive-oil wastewater resulted in an overall biogas production of 2·28 litres/litre working volume and in an overall COD reduction of 94·02% with a final COD concentration of 4000 mg/litre olive-oil wastewater. The results indicated that a total reactor volume of 9·2 litres/ litre wastewater was required, 4·08 litres for the fixed-bed and 5·12 litres for the plug-flow digesters. In this way, the anaerobic-digestion system suggested is of reduced size and becomes cost-effective compared with other digestion systems suggested in the literature for such wastes.

Sulfate Reduction Relative to Methane Production in High-Rate Anaerobic Digestion: Microbiological Aspects

In the high-rate anaerobic reactors studied (ca. 10 g of chemical oxygen demand [COD] removed per liter of reactor per day), the sulfate-reducing bacteria (SRB) were poor competitors of methane-producing bacteria (MPB), scavenging only on the order of 10 to 20% of the total electron flow. The relatively noncompetitive nature of the SRB in this type of reactor is in sharp contrast to the tendency of the SRB to dominate in natural environments and in other types of anaerobic digesters. Various factors such as the feedback inhibition of H(2)S on the SRB, iron limitation, the origin of the SRB inocula, biokinetics, and thermodynamics were investigated. The outcome of the SRB-MPB competition under the reactor conditions studied appeared to be particularly determined by two factors. The SRB, as predicted by the V(max)-K(m) kinetics, competed most effectively at low substrate levels (<0.5 g of COD per liter). The MPB, however, appeared to colonize and adhere much more effectively to the polyurethane carrier matrix present in the reactor, thus compensating for the apparent lower growth rates. Even if the reactor was initially allowed to be predominantly colonized by SRB, the MPB could regain dominance.