Solids and nutrients removals from the liquid fraction of swine slurry through screening and flocculation treatment and influence of these processes on anaerobic biodegradability

A correct separation of solids from liquid fraction is crucial for a successful treatment of swine manure. For this reason an in-depth study of flocculant addition on different livestock wastewaters was carried out. Two flushed swine manure matrices, namely the mixture from nursery and feeder-to-finish pigs and the feeder-to-finish slurry alone, were tested for solids and nutrients removals from liquid fractions. The separation techniques applied were sieving and flocculation. A range of 80-200 ppm of polyacrylamide (PAM) followed by screening was employed in the case of flocculation treatment. The best results were observed when using the highest PAM dose in the matrix correspondent to the mixture of slurries. The removal rates in the liquid fraction were 73% for total solids, 87% for volatile solids, 98% for suspended total and volatile solids, 71% for chemical oxygen demand, 40% for total Kjeldahl nitrogen, and 34% for soluble phosphorus. Once the best PAM dose (120 ppm) was chosen, an anaerobic biodegradability study was performed in order to check the increase of methane production in the separated fractions by using the flocculant and the screen. The assay determined that the solid fractions biodegradability was constant at 79%. Meanwhile for the liquid fractions, an increase of 9% points was achieved with PAM-amendment when compared with 82% reached for the liquid fraction obtained by screening.     

Impact of milling,enzyme addition,and steam explosion on the solid waste biomethanation of an olive oil production plant

Anaerobic digestion is a consolidated bioprocess which can be further enhanced by incorporating an upstream pretreatment unit. The olive oil production produces a large amount of solid waste which needs to be properly managed and disposed. Three different pretreatment techniques were evaluated in regard to their impact on the anaerobic biodegradability: manual milling of olive pomace (OP), enzyme maceration, direct enzyme addition, and thermal hydrolysis of two-phase olive mill waste. The Gompertz equation was used to obtain parameters for comparison purposes. A substrate/inoculum ratio 0.5 was found to be the best to be used in anaerobic batch test with olive pomace as substrate. Mechanical pretreatment of OP by milling increases the methane production rate while keeping the maximum methane yield. The enzymatic pretreatment showed different results depending on the chosen pretreatment strategies. After the enzymatic maceration pretreatment, a methane production of 274 ml CH₄ g VS _added ^?1 was achieved, which represents an improvement of 32 and 71 % compared to the blank and control, respectively. The direct enzyme addition pretreatment showed no improvement in both the rate and the maximum methane production. Steam explosion showed no improvement on the anaerobic degradability of two-phase olive mill waste; however, thermal hydrolysis with no rapid depressurization enhanced notoriously both the maximum rate (50 %) and methane yield (70 %).     

Enhancing the solid-state anaerobic digestion of fallen leaves through simultaneous alkaline treatment

Previous studies have shown that alkali pretreatment prior to anaerobic digestion (AD) can increase the digestibility of lignocellulosic biomass and methane yield. In order to simplify the process and reduce the capital cost, simultaneous alkali treatment and anaerobic digestion was evaluated for methane production from fallen leaves. The highest methane yield of 82 L/kg volatile solids (VS) was obtained at NaOH loading of 3.5% and substrate-to-inoculum (S/I) ratio of 4.1. The greatest enhancement in methane yield was achieved at S/I ratio of 6.2 with NaOH loading of 3.5% which was 24-fold higher than that of the control (without NaOH addition). Reactors at S/I ratio of 8.2 resulted in failure of the AD process. In addition, increasing the total solid (TS) content from 20% to 26% reduced biogas yield by 35% at S/I ratio of 6.2 and NaOH loading of 3.5%. Cellulose and hemicellulose degradation and methane yields are highly related.     

Methane production from rice straw pretreated by a mixture of acetic–propionic acid

Rice straw was treated with a mixed solution of acetic acid and propionic acid to enhance its biodegradability. The effect of acid concentration, pretreatment time, and the ratio of solid to liquid on the delignification performance of rice straw were investigated. It was found that the optimal conditions for hydrolysis were 0.75 mol/L acid concentration, 2 h pretreatment time and 1:20 solid to liquid ratio. Batch methane fermentation of untreated rice straw, pretreated rice straw, and the hydrolysates (the liquid fraction) of pretreatment were conducted at 35 °C for 30 days, and the results indicated that methane production of rice straw can be enhanced by dilute organic acid pretreatment. Moreover, most of the acid in hydrolysates can also be converted into methane gas.     

Effect of biological pretreatments in enhancing corn straw biogas production

A biological pretreatment with new complex microbial agents was used to pretreat corn straw at ambient temperature (about 20°C) to improve its biodegradability and anaerobic biogas production. A complex microbial agent dose of 0.01% (w/w) and pretreatment time of 15 days were appropriate for biological pretreatment. These treatment conditions resulted in 33.07% more total biogas yield, 75.57% more methane yield, and 34.6% shorter technical digestion time compared with the untreated sample. Analyses of chemical compositions showed 5.81-25.10% reductions in total lignin, cellulose, and hemicellulose contents, and 27.19-80.71% increases in hot-water extractives; these changes contributed to the enhancement of biogas production. Biological pretreatment could be an effective method for improving biodegradability and enhancing the highly efficient biological conversion of corn straw into bioenergy.     

Production and characterization of β-glucosidase from Aspergillus niger fermentation: Application for organic fraction of municipal solid waste hydrolysis and methane enhancement

The anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) is currently an attractive treatment process with energy production in the form of biogas. Hydrolysis is the rate-limiting step for the anaerobic digestion of solid wastes. Thus, in the present study fungal enzymatic pretreatment of OFMSW was applied to enhance biogas production. Two enzyme cocktails rich on β-glucosidase were produced from submerged fermentation of Aspergillus niger on basal medium using OFMSW as carbon source and urea (Urea cocktail) and Ulva rigida as nitrogen source (Ulva cocktail). Ulva cocktail displayed an important effect on OFMSW solubilization. Therefore, an increase of reducing sugar concentration about 60% was obtained which was in correlation with chemical oxygen demand (COD) increase. The performance of enzymatic pretreatment on anaerobic digestion of OFMSW was studied by conducting biochemical methane potential tests. Results showed that the enzymatic pretreatment improved methane yield of OFMSW even at high solid concentration. High methane yield about 500 ml/g total volatile solid was obtained, which corresponds up to 68% enhancement over the control.     

Enhancement of biochemical methane potential from excess sludge with low organic content by mild thermal pretreatment

Excess sludge with low organic content always led to the failure of anaerobic digestion for methane production. Recently, the mild thermal pretreatment, which is usually operated at temperatures below 120 °C, has drawn much attention due to less energy consumption and no chemical addition. In this study the effect of mild thermal pretreatment (50–120 °C) on the solubilization and methane potential of excess sludge with a low concentration of organic matters was investigated. Experimental results showed that the concentration of soluble organic matters increased gradually with temperature during the mild thermal pretreatment of excess sludge. Biochemical methane potential experiments demonstrated that the potential of methane production from excess sludge was greatly enhanced by mild thermal pretreatment, and under the conditions of pretreatment temperature 100 °C and digestion time 20 d the methane yield was as high as 142.6 ± 2.5 mL/g of volatile solids. Mechanism investigation on the enhancement of methane production from excess sludge exhibited that the consumptions of sludge protein and carbohydrate, the adenosine 5′-triphosphate content of anaerobic microorganisms, the activities of key enzymes related to anaerobic digestion, and the amount of methanogens were all improved by mild thermal pretreatment, in correspondence with the production of methane.     

Impact of pretreatment on solid state anaerobic digestion of yard waste for biogas production

Solid state anaerobic digestion, as a safe and environment-friendly technology to dispose municipal solid wastes, can produce methane and reduce the volume of wastes. In order to raise the digestion efficiency, this study investigated the pretreatment of yard waste by thermal or chemical method to break down the complex lignocellulosic structure. The composition and structure of pretreated yard waste were analyzed and characterized. The results showed that the pretreatment decreased the content of cellulose and hemicelluloses in yard waste and in turn improved the hydrolysis and methanogenic processes. The thermal pretreatment sample (P1) had the highest methane yield, by increasing 88 % in comparison with digesting the raw material. The maximum biogas production reached 253 mL/g volatile solids (VS). The largest substrate mass reduction was obtained by the alkaline pretreatment (P5). The VS of the alkaline-treated sample decreased about 60 % in comparison with the raw material.     

Feasibility study of the anaerobic digestion of dewatered pig slurry by means of polyacrylamide

Liquid livestock waste can be managed by separating liquid and solid fractions then treating each separately by applying best available technology, such as anaerobic digestion for the solid fraction. There is an increasing use of polyacrylamide (PAM) as a flocculant agent to improve solid-liquid separation. In the present work, the anaerobic toxicity of PAM residues and the optimal range of total solids concentration for maximum methane production were studied as a function of PAM dosage. Results showed that dry matter and its volatile solids content increased significantly with increasing PAM dosage. Batch anaerobic tests showed that methane yield decreased linearly with increasing total solids, while the methane production per unit of raw substrate reached a maximum at 16.4% total solids. No PAM toxicity was measured for PAM concentrations below 415 g/kg total solids, but some indirect inhibitory phenomena were observed, such as a limited hydrolysis rate due to particle aggregation, and inhibition of methanogenesis by high ammonia concentration.     

Characterisation of solid and liquid fractions of dairy manure with regard to their component distribution and methane production

Dairy manure with a total solids content of 77.2g TS/l was separated by means of screening and coagulation-flocculation treatments, using CaO as coagulant and a cationic polyacrylamide as flocculant, obtaining liquid and solid fractions. The solid fraction separated contained 33.4% of the initial total mass of dairy manure plus chemical solutions, containing also 75.2% of the TS, 80.4% of the VS, 58.5% of the total Kjeldahl nitrogen (TKN) and 87.4% of the total phosphorus (P(T)) present in the initial dairy manure. 83.7% of the liquid fraction chemical oxygen demand (COD) was anaerobically biodegradable (COD(BD)). Methane production for the separated liquid fraction was 0.604l CH4 NCTP/g VS added, being 0.307 and 0.371l CH4 NCTP/g VS added for dairy manure and screened dairy manure, respectively. The characteristics of this liquid fraction would allow its treatment in high loading anaerobic reactors having shorter hydraulic retention times, smaller reactor size and a higher methane volumetric production rate than conventional anaerobic reactors treating either manure or screened manure.     

Modeling alkali consumption and digestibility improvement from alkaline treatment of wheat straw

The alkali consumption during alkaline treatment of wheat straw at ambient temperature was measured as a function of time, solids concentration, and alkali concentration. The maximum measured alkali consumption was 5.5 g NaOH/100 g TS over a period of 30 days of treatment. Chemical functional groups (e.g., acyl and carboxyl groups) were measured and compared with the observed alkali consumption. The kinetics of alkali consumption were studied and a model was developed which predicts alkali consumption reasonably well. Use of this model was made to predict biodegradability of alkali-treated wheat straw, since a strong correlation was found to exist between alkali consumption and observed biodegradability. The method of bioconversion used was anaerobic digestion for methane production.     

Alkaline treatment of wheat straw for increasing anaerobic biodegradability

Wheat straw was treated with NaOH and anaerobically digested for methane production. Alkaline treatment resulted in a greater than 100% increase in biodegradability of wheat straw. The potential of a process flow scheme employing high alkali concentration at ambient temperature with solids separation and recycle of filtrate containing residual alkali was explored. The effect of NaOH on the solubilization of cell wall constituents and potential problems of toxicity are discussed. A solubilization model was developed which is used to predict biodegradability of whole samples based on solids and filtrate biodegradabilities. Energy requirements and chemical costs are also addressed.     

Optimisation of a microwave pretreatment of wheat straw for methane production

This study aims at the optimisation of a microwave pretreatment for wheat straw solubilisation and anaerobic biodegradability. The maximum yield of methane production was obtained at 150 °C with an improvement of 28% compared to an untreated sample. In addition, at this temperature, the time to reach 80% of the methane volume obtained from untreated straw was about 35%. The study of ramp time and holding time at targeted temperature showed that they had no improvement effect. Thus, the best conditions are the highest heating rate for a final temperature 150 °C without any holding time. The reading of energy consumed by pretreatment and energy overproduced by pretreated samples showed that increasing tVS amount and heating rate led to a saving of energy consumption. Nevertheless, to obtain a positive energy balance, a microwave device should consume less than 2.65 kJ/g_tVS.     

Anaerobic co-digestion of sewage sludge and grease trap: Assessment of enzyme addition

Anaerobic co-digestion of grease trap and sewage sludge from a wastewater treatment plant is evaluated. Enzyme-lipase application, both addition and dosage, are evaluated by fitting the methane production of biochemical potential tests with the first order model. The enzyme addition effect, at 2, 5 and 10% of grease trap (%GT VS_FED^?1) and the enzymes doses, between 0.25 and 1.67% (v/v), without and with grease trap presence were studied. Grease trap addition showed a negative effect on the waste biodegradability, which was completely overcome by the addition of lipase. Enzyme addition improved notably the methane production for all grease trap fractions studied. In regards to the dosage, the best result was achieved between 0.33 and 0.83% (v/v) of enzyme. The co-digestion of sewage sludge and grease trap may be a feasible process by using lipases due to the saving in operational costs and the increase in the biogas production     

Ultrasonic and Thermal Pretreatments on Anaerobic Digestion of Petrochemical Sludge: Dewaterability and Degradation of PAHs

Effects of different pretreatment methods on sludge dewaterability and polycyclic aromatic hydrocarbons (PAHs) degradation during petrochemical sludge anaerobic digestion were studied. Results showed that the total biogas production volume in the thermal pretreatment system was 4 and 5 times higher than that in the ultrasound pretreatment and in the control system, and the corresponding volatile solid removal efficiencies reached 28%, 15%, and 8%. Phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene removal rates reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, respectively, in the thermal pretreatment system, which were much higher than those in the ultrasound pretreatment and in the control system. Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion. The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion. This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.     

Enhancing anaerobic biogasification of corn stover through wet state NaOH pretreatment

A new method of wet state (WS) sodium hydroxide (NaOH) was advanced to pretreat corn stover for enhancing biogas production. The results showed that 88% moisture content, 3-day treatment time and ambient temperature (20 °C) was appropriate for WS NaOH pretreatment. The NaOH dose of 2% and the loading rate of 65 g/L were found to be optimal in terms of 72.9% more total biogas production, 73.4% more methane yield, and 34.6% shorter technical digestion time, as compared to the untreated one. WS pretreatment used 86% shorter treatment time and 66.7% less NaOH dose than solid state one. The analyses of chemical compositions and chemical structures showed that 9.3–19.1% reduction of the contents of total Lignin, cellulose, and hemicellulose (LCH), and 27.1–77.1% increase of hot-water extractives contributed to the enhancement of biogas production. WS NaOH pretreatment could be one of cost-effective methods for high efficient biological conversion of corn stover into bioenergy.     

Alternative methods for determining anaerobic biodegradability: A review

The characterization of solid wastes is a necessary step before they can be used in anaerobic digestion. The quantities of different compounds (carbohydrates, proteins, lipids and fibers) and anaerobic biodegradability (capacity to produce methane) are important information required to characterize waste. The Biochemical Methane Potential (BMP) test is one of the most relevant tests for assessing the biodegradability of waste materials. The BMP test is run under anaerobic conditions, using bacteria populations, which makes it very time consuming, i.e., about 30 days. This paper presents alternative methods for determining the anaerobic biodegradability of solid waste. First, we describe the already existing tests for characterizing organic matter. Then we correlate an aerobic test with an anaerobic test in order to estimate anaerobic biodegradability and biogas production. This shortens the analysis time to 5 days. Models using physico-chemical characteristics as input data (total carbohydrate, total nitrogen, fiber, etc.) can predict the amount of methane produced by correlation. Pyrolysis is a very fast analytical test that can be used to characterize solid waste. Lastly, spectroscopy techniques seem to be useful for determining biodegradability, in particular by taking into account the interaction between different molecules in the organic matter.     

Dilute acid pretreatment of rye straw and bermudagrass for ethanol production

Ethanol production from lignocellulosic materials provides an alternative energy production system. Rye and bermudagrass that are used in hog farms for nutrient uptake from swine wastewater have the potential for fuel ethanol production because they have a relative high cellulose and hemicellulose content. Dilute sulfuric acid pretreatment of rye straw and bermudagrass before enzymatic hydrolysis of cellulose was investigated in this study. The biomass at a solid loading rate of 10% was pretreated at 121 degrees C with different sulfuric acid concentrations (0.6, 0.9, 1.2 and 1.5%, w/w) and residence times (30, 60, and 90 min). Total reducing sugars, arabinose, galactose, glucose, and xylose in the prehydrolyzate were analyzed. In addition, the solid residues were hydrolyzed by cellulases to investigate the enzymatic digestibility. With the increasing acid concentration and residence time, the amount of arabinose and galactose in the filtrates increased. The glucose concentration in the prehydrolyzate of rye straw was not significantly influenced by the sulfuric acid concentration and residence time, but it increased in the prehydrolyzate of bermudagrass with the increase of pretreatment severity. The xylose concentration in the filtrates increased with the increase of sulfuric acid concentration and residence time. Most of the arabinan, galactan and xylan in the biomass were hydrolyzed during the acid pretreatment. Cellulose remaining in the pretreated feedstock was highly digestible by cellulases from Trichoderma reesei.     

Solids,organic load and nutrient concentration reductions in swine waste slurry using a polyacrylamide (PAM)-aided solids flocculation treatment

Increased swine production results in concentration of wastes generated within a limited geographical area, which may lead to land application rates exceeding the local or regional assimilatory capacity. This may result in pollutant transfer through surface water or soil-groundwater systems, environmental degradation, and/or odor concerns. Existing swine waste pit storage and lagoon treatment technologies may be inadequate to store or treat waste prior to land application without these concerns resulting. Efficient swine waste solids separation may reduce environmental health concerns and generate a value-added bioresource (solids). This study evaluated the efficiency of a polyacrylamide (PAM) flocculant-aided solids separation treatment to reduce pollution indicator concentrations in raw (untreated) swine waste slurry. Swine waste slurry solids separation efficiency through gravity settling (sedimentation) was evaluated before and after the addition of a proprietary polymeric (PAM) flocculant. Results indicated that polymer amendments at concentrations of 62.5-750 mg/l improved slurry solids separation efficiency and significantly reduced concentrations of other associated aquatic pollution indicators in a majority of analyses conducted (33 of 50 total analyses conducted). Results also suggested that PAM-aided solids separation from swine waste slurry might facilitate further treatment and/or disposal and therefore reduce associated environmental degradation potential.     

Pretreatment of pulp mill secondary sludge for high-rate anaerobic conversion to biogas

Three pretreatment methods were compared based on their ability to increase the extent and rate of anaerobic bioconversion of pulp mill secondary sludge to biogas. The pretreatment technologies used in these experiments were: (i) thermal pretreatment performed at 170 °C; (ii) thermochemical (caustic) pretreatment performed at pH 12 and 140 °C; and (iii) sonication performed at 20 kHz and 1 W mL⁻¹. Sludge samples were obtained from a sulfite and a kraft pulp mill, and biochemical methane potential (BMP) assays were performed using microbial granules obtained from a high-rate anaerobic digester operating at a pulp mill. Biogas production from untreated sludge was 0.05 mL mg⁻¹ of measured chemical oxygen demand (COD) and 0.20 mL mg⁻¹ COD for kraft and sulfite sludge, respectively. Thermal pretreatment had the highest impact on sludge biodegradability. In this case, biogas yield and production rate from sulfite sludge increased by 50% and 10 times, respectively, while biogas yield and production rate from kraft sludge increased by 280% and 300 times, respectively. Biogas yield correlated to soluble carbohydrate content better than soluble COD.