Annop Nopharatana

Evaluation of methanogenic activities during anaerobic digestion of municipal solid waste

Numerous researchers have demonstrated that the rate and extent of the degradation of municipal solid waste (MSW) can be enhanced beyond that observed in a conventional landfill by adding moisture, buffering agents and sources of microorganisms such as anaerobically digested sludge. One method of achieving the addition of these agents is by directing leachate that has trickled through a bed of anaerobically stabilised waste to beds of fresh MSW. Proper operational strategies need to be developed for successful implementation of this process on a large scale or in a landfill. Operational parameters of primary importance are the point of time at which a stabilised waste bed can be used for sequencing, the period of sequencing and the minimal amount of leachate that has to be recirculated to rapidly attain balanced microbial activity in a fresh waste bed. Assays that measure a substrate-specific methanogenic activity of an anaerobic microbial consortia have been previously developed by researchers. These assays were employed in this study to evaluate the microbial activity of the leachate for utilisation of substrates like cellulose, acetate and formate. Activity in leachate samples, taken from a batch of MSW at various times during the degradation process, was measured in terms of the amount of methane produced in 4 h after spiking the sample with one of the selected substrates. Activity resulting from the utilisation of formate and cellulose showed considerable promise as indicators for optimising operational strategies. It was observed that the formate degradation activity followed the methane production rate with both reaching a maximum at the same time and that this could be used as an indicator for determining the period of sequencing. Cellulase activity in fresh waste beds responded to flushes of mature leachate and peaked a few days after sequencing was terminated.

Cellulolytic activity in leachate during leach-bed anaerobic digestion of municipal solid waste

The degradation of municipal solid waste (MSW) under mesophilic conditions can be enhanced by exchanging leachate between fresh waste and stabilised waste. The optimum point in time when leachate from an anaerobically digesting waste bed can be used to initiate degradation of another waste bed might occur when the leachate of the digesting waste bed is highly active with cellulolytic and methanogenic bacteria. In this study, the cellulolytic activity of the leachate was measured using the cellulose-azure assay. As products of hydrolysis are soluble compounds, the rate of generation of these compounds was estimated based on a soluble chemical oxygen demand (SCOD) balance around the fresh waste bed. It was found that once the readily soluble material present in MSW was washed out there was very little generation of SCOD without the production of methane, indicating that flushing leachate from a stabilised waste bed resulted in a balanced inoculation of the fresh waste bed. With the onset of sustained methanogenesis, the rate of SCOD generation equalled the SCOD released from the digester as methane. The experimental findings also showed that cellulolytic activities of the leachate samples closely followed the trend of SCOD generation. reserved.

A dynamic mathematical model for sequential leach bed anaerobic digestion of organic fraction of municipal solid waste

A mathematical model that describes the operation of a sequential leach bed process for anaerobic digestion of organic fraction of municipal solid waste (MSW) is developed and validated. This model assumes that ultimate mineralisation of the organic component of the waste occurs in three steps, namely solubilisation of particulate matter, fermentation to volatile organic acids (modelled as acetic acid) along with liberation of carbon dioxide and hydrogen, and methanogenesis from acetate and hydrogen. The model incorporates the ionic equilibrium equations arising due to dissolution of carbon dioxide, generation of alkalinity from breakdown of solids and dissociation of acetic acid. Rather than a charge balance, a mass balance on the hydronium and hydroxide ions is used to calculate pH. The flow of liquid through the bed is modelled as occurring through two zones-a permeable zone with high flushing rates and the other more stagnant. Some of the kinetic parameters for the biological processes were obtained from batch MSW digestion experiments. The parameters for flow model were obtained from residence time distribution studies conducted using tritium as a tracer. The model was validated using data from leach bed digestion experiments in which a leachate volume equal to 10% of the fresh waste bed volume was sequenced. The model was then tested, without altering any kinetic or flow parameters, by varying volume of leachate that is sequenced between the beds. Simulations for sequencing/recirculating 5 and 30% of the bed volume are presented and compared with experimental results

Neural-fuzzy control system application for monitoring process response and control of anaerobic hybrid reactor in wastewater treatment and biogas production

Based on the developed neural-fuzzy control system for anaerobic hybrid reactor (AHR) in wastewater treatment and biogas production, the neural network with backpropagation algorithm for prediction of the variables pH, alkalinity (Alk) and total volatile acids (TVA) at present day time t was used as input data for the fuzzy logic to calculate the influent feed flow rate that was applied to control and monitor the process response at different operations in the initial, overload influent feeding and the recovery phases. In all three phases, this neural-fuzzy control system showed great potential to control AHR in high stability and performance and quick response. Although in the overloading operation phase II with two fold calculating influent flow rate together with a two fold organic loading rate (OLR), this control system had rapid response and was sensitive to the intended overload. When the influent feeding rate was followed by the calculation of control system in the initial operation phase I and the recovery operation phase III, it was found that the neural-fuzzy control system application was capable of controlling the AHR in a good manner with the pH close to 7, TVA/Alk < 0.4 and COD removal > 80% with biogas and methane yields at 0.45 and 0.30 m3/kg COD removed.

Enhancement of biogas production from swine manure by a lignocellulolytic microbial consortium.

Anaerobic digestion of lignocellulosic wastes is limited by inefficient hydrolysis of recalcitrant substrates, leading to low biogas yield. In this study, the potential of a lignocellulolytic microbial consortium (LMC) for enhancing biogas production from fibre-rich swine manure (SM) was assessed. Biochemical methane potential assay showed that inoculation of structurally stable LMC to anaerobic digestion led to increase biogas production under mesophilic and thermophilic conditions. The greatest enhancement was observed at 37°C with a LMC/SM ratio of 1.5:1 mg VSS/g VS leading to biogas and methane yields of 355 and 180 ml/g VS(added) respectively, equivalent to 40% and 55% increases compared with the control. The LMC was shown to increase the efficiency of total solid, chemical oxygen demand removal and degradation of cellulose and hemicelluloses (1.87 and 1.65-fold, respectively). The LMC-supplemented process was stable over a 90 d biogas production period. This work demonstrates the potential of LMC for enhancing biogas from lignocellulosic wastes.

Combination effect of pH and acetate on enzymatic cellulose hydrolysis.

The productivity and efficiency of cellulase are significant in cellulose hydrolysis. With the accumulation of volatile fatty acids (VFAs), the pH value in anaerobic digestion system is reduced. Therefore, this study will find out how the pH and the amount of acetate influence the enzymatic hydrolysis of cellulose. The effects of pH and acetate on cellulase produced from Bacillus coagulans were studied at various pH 5-8, and acetate concentrations (0-60 mmol/L). A batch kinetic model for enzymatic cellulose hydrolysis was constructed from experimental data and performed. The base hypothesis was as follows: the rates of enzymatic cellulose hydrolysis rely on pH and acetate concentration. The results showed that the suitable pH range for cellulase production and cellulose hydrolysis (represents efficiency of cellulase) was 2.6-7.5, and 5.3-8.3, respectively. Moreover, acetate in the culture medium had an effect on cellulase production (K(I) = 49.50 mmol/L, n = 1.7) less than cellulose hydrolysis (K(I) = 37.85 mmol/L, n = 2.0). The results indicated that both the pH of suspension and acidogenic products influence the enzymatic hydrolysis of cellulose in an anaerobic environment. To enhance the cellulose hydrolysis rate, the accumulated acetate concentration should be lower than 25 mmol/L, and pH should be maintained at 7.

Microbial community structure and performance of an anaerobic reactor digesting cassava pulp and pig manure

Microbial community dynamics in response to changes in substrate types (i.e. pig manure (PM), cassava pulp (CP) and mixtures of PM and CP) were investigated in an anaerobic continuously stirred tank reactor (CSTR). Molecular identification of bacterial and archaeal domains were performed, using a 16S rDNA clone library with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) screening and phylogenetic analysis. Analysis of bacterial clone libraries revealed that the differences in the community structure corresponded to the substrate types. However, the Bacteroidetes were the most abundant group in all substrates, followed by the Clostridia. With pure PM, the dominant bacterial groups were Bacteroidales, Clostridia and Paludibacter. With a co-substrate, at CP to PM (CP:PM) ratio of 50:50, the sequences analysis revealed the greatest diversity of bacterial communities at class level, and the sequences affiliated with Cytophaga sp. became an exclusive predominant. With CP alone, Bacteroides sp. was the dominant species and this reactor had the lowest diversity of bacteria. Archaea observed in the CSTR fed with all substrate types were Methanosaeta sp., Methanosaeta concilii and Methanospirillum hungatei. Among the Archaea, Methanosaeta sp. was the exclusive predominant. The relative distribution of Archaea also changed regarding to the substrate types.

Effect of recirculation rate on methane production and SEBAR system performance using active stage digester

A project was undertaken to examine the feasibility of treating organic wastes from Thai fruit and vegetable markets using the sequential batch anaerobic digester (SEBAR) approach. A key feature of the SEBAR system is the regular interchanging, or recirculation, of portions of leachate between each freshly filled digester and a support digester to which it is coupled until it is ready to operate independently. Leachate transfer from this support digester to the fresh waste digester provides additional alkalinity to help counteract the effects of early high acid release rates; it also helps build a balanced microbial population in the fresh waste digester. To optimize the leachate recirculation process, the effect of varying the quantities of leachate interchanged between freshly filled waste digesters and the still highly active support digesters to which they were coupled was studied. It was found that increasing the recirculation rate accelerated the onset of both waste degradation and methane production. The increasing of recirculation rate from 10% to 20% and 10% to 30% could reduce the SEBAR cycle period by approximately 7% and 22% without significant reduction in the amount of methane obtained from the systems. The methane yields were 0.0063, 0.0068 and 0.0077 l g—1 VS added in the NEW digester per day using leachate recirculation rates of 10%, 20% and 30%, respectively. This finding has potentially important practical and economic implications for those using the SEBAR system to add value to market waste.

Development of an Oscillating Drum Granulator Prototype for Cassava Pearl

This paper presents an oscillating drum granulator prototype for cassava pearl. Effects of filling degree and oscillating speed on cassava pearl granulation were investigated. A stainless steel drum granulator with 50 cm diameter and 16 cm length was developed. The stainless steel joints with a cotton-transmitting belt were used to connect the drum to an oscillator arm to simulate the flexibility of a traditional cloth cradle granulator. The filling degree and oscillating speed were varied from 1, 2 and 3 kg and from 87 and 100 rpm, respectively. During granulation, samples were taken at 4, 8, 12 and 16 minutes to determine the particle size distribution, mass mean diameter, granule density, hardness and sphericity. The results indicated that both the filling degree and oscillating speed played an important role on cassava pearl granulation. The filling degree of 3 kg and oscillating speed of 100 rpm was suggested since it yielded similar properties of cassava pearls to those obtained from the traditional process. This prototype granulator could successfully produce 2.4-mm pearls with comparable characteristics to the standards. Comparing to a traditional granulator, the oscillating drum granulator is easier to clean and more GMP compliant.

Effects of Pneumatic Conveying Drying Conditions on Damaged Starch Content and Particle Size of Cassava Starch

This research aimed to investigate the effects of pneumatic conveying drying conditions on damaged starch content and particle size of cassava starch using response surface methodology. Three parameters of interest, i.e. drying air temperature (120, 160, and 200oC), drying air velocity (20, 30, and 40 m/s), and feed moisture content (40, 50, and 60% d.b.), were varied. Experimental results showed that damaged starch content and average particle size of cassava starch before drying were approximately 0.45% and 21.47µm, respectively. However, after drying, the values were altered to approximately 0.69 to 6.84% and 15.40 to 31.67 µm, respectively. The drying air temperature, drying air velocity, and feed moisture content significantly affected the changes. The results indicated that cassava starch granules were damaged and then agglomerated into large particle during pneumatic conveying drying depending on operation conditions.