B. Rincón

Evaluation of the hydrolytic–acidogenic step of a two-stage mesophilic anaerobic digestion process of sunflower oil cake

The influence of the hydraulic retention time (HRT) and organic loading rate (OLR) on the performance of the hydrolytic-acidogenic step of a two-stage anaerobic digestion process of sunflower oil cake (SuOC) were assessed. The experiments were performed in laboratory-scale completely stirred tank reactors at mesophilic (35 degrees C) temperature. Six OLR (ranging from 4 to 9 g VS L(-1) d(-1)) for four HRTs (8, 10, 12 and 15 days) were tested to check the effect of each operational variable. Based on the results obtained, it can be concluded that the hydrolysis yields obtained for all HRTs and OLRs assayed were in the range of 20.5-30.1%. In addition, the acidification degree of the substrate was mainly influenced by the OLR but not by the HRTs, the highest value (83.8%) being achieved for an HRT of 10 days and an OLR of 6 g VS L(-1) d(-1).

A study of anaerobic digestibility of two-phases olive mill solid waste (OMSW) at mesophilic temperature

A study of the anaerobic digestibility of two-phases olive mill solid waste (OMSW) was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 °C). The reactor was operated at influent substrate concentrations of 34.5 g COD/l (OMSW 20%), 81.1 g COD/l (OMSW 40%), 113.1 g COD/l (OMSW 60%) and 150.3 g COD/l (OMSW 80%). The hydraulic retention time (HRT) varied between 40.0 and 8.3 days for the first feed used (OMSW 20%) and between 50 and 10 days for the other three influent substrate concentrations. Chemical oxygen demand (COD) and volatile solids (VS) removal efficiencies of 88.4 and 90.9%, respectively, were achieved at an organic loading rate (OLR) of 12.02 g COD/l day for the most concentrated substrate used (OMSW 80%). The maximum methane production rate was found to be 2.12 l CH4/l day for the above-mentioned OLR and a HRT of 12.5 days. The system can tolerate OLRs as high as 15.03 g COD/l day with COD and VS removal efficiencies of 82.9 and 86.6%, respectively, for this feed concentration. The methane yield coefficients were 0.30, 0.27, 0.23 and 0.20 l methane STP/g COD removed for the OMSW concentrations of 20, 40, 60 and 80%, respectively.

Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence of growth stage and storage practice

The effect of growth stage at harvest and of storage practice on the biochemical methane potential (BMP) of winter wheat was investigated using batch-fed stirred mesophilic digesters. The wheat used was a single variety sown at the same time (autumn) and harvested at 3 different stages in its growth: medium milk (A), soft dough (B) and Caryopsis (C). Wheats (A and B) were ensiled whilst the later harvested material (C) with a higher dry matter content was treated by the alkalage process. The BMP values expressed on the basis of volatile solids (VS) were 0.360 + or - 0.030, 0.346 + or - 0.006 and 0.311 + or - 0.016l CH(4) g(-1) VS(added) for A, B and C, respectively. A simple first order kinetic model gave only a poor fit to the experimental data but a close match was obtained using a modified first order pseudo-parallel model which explains the methane production curve on the basis of differences in biodegradability of the plant material.

Evaluation of the methanogenic step of a two-stage anaerobic digestion process of acidified olive mill solid residue from a previous hydrolytic-acidogenic step.

A study of the second step or methanogenic stage of a two-stage anaerobic digestion process treating two-phase olive oil mill solid residue (OMSR) was conducted at mesophilic temperature (35 degrees C). The substrate fed to the methanogenic step was the effluent from a hydrolytic-acidogenic reactor operating at an organic loading rate (OLR) of 12.9 g chemical oxygen demand (COD) L(-1) d(-1) and at a hydraulic retention time (HRT) of 12.4 days; these OLR and HRT were found to be the best values to achieve the maximum total volatile fatty acid concentration (14.5 g L(-1) expressed as acetic acid) with a high concentration in acetic acid (57.5% of the total concentration) as the principal precursor of methane. The methanogenic stage was carried out in an anaerobic stirred tank reactor containing saponite as support media for the immobilization of microorganisms. OLRs of between 0.8 and 22.0 g COD L(-1) d(-1) were studied. These OLRs corresponded to HRTs of between 142.9 and 4.6 days. The methanogenic reactor operated with high stability for OLRs lower than 20.0 g COD L(-1) d(-1). This behaviour was shown by the total volatile fatty acids/total alkalinity ratio, whose values were always kept 0.12 for HRTs>4.6 days. The total COD (T-COD) removed was in the range of 94.3-61.3% and the volatile solids (VS) removed between 92.8% and 56.1% for OLRs between 0.8 and 20.0 g COD L(-1) d(-1). In the same way, a reduction of 43.8% was achieved for phenolic content. The low concentration of total volatile fatty acids (TVFA) observed (below 1 g L(-1) expressed as CH(3)COOH) in the methanogenic reactor effluents showed the high percentage of consumption and conversion of these acids to methane. A methane yield of 0.268+/-0.003 L CH(4) at standard temperature and pressure conditions (STP) g(-1) COD eliminated was achieved.

Biochemical methane potential of two-phase olive mill solid waste: Influence of thermal pretreatment on the process kinetics

The effect of thermal pretreatment on two-phase olive mill solid waste was evaluated by chemical oxygen demand solubilisation and biochemical methane potential (BMP) tests. Temperatures of 100, 120, 160 and 180°C were applied during 60, 120 and 180 min for each temperature studied. The highest chemical oxygen demand solubilisation after pretreatment (42%) was found for 120 and 180°C during 180 min in both cases. These two conditions were selected for the BMP tests. BMP tests showed two different stages: a first exponential stage and a sigmoidal zone after a lag period. No influence of the pretreatment was observed on the kinetic constant of the first-stage. Clear difference was observed in the maximum methane production rate of the second stage, 76.8 mL CH4/(g VS day) was achieved after pretreatment at 180°C (180 min), value 22% and 40% higher than that obtained for the untreated and pretreated OMSW at 120°C, respectively.

Assessment of two-phase olive mill solid waste and microalgae co-digestion to improve methane production and process kinetics

Olive mill solid waste (OMSW) is a pollutant waste coming from olive oil elaboration by the two-phase centrifugation system. OMSW has a high organic matter content and unbalanced carbon to nitrogen (C/N) ratio, 31/1, which avoids obtaining high methane yields in the anaerobic digestion of this waste. In the present study a microalgae, Dunaliella salina, was employed as co-substrate for the OMSW anaerobic digestion in order to decrease the C/N ratio and increase its biodegradability. Different co-digestion mixtures (C/N ratios) were studied. The increase of D. salina from 25% to 50% in the co-digestion mixture clearly increased the biodegradability of the sole substrates. The highest biodegradability was found for the co-digestion mixture 50% OMSW-50% D. salina. Nevertheless, the maximum methane production, 330mLCH4/gVSadded, and the highest methane production rate were obtained for the co-digestion mixture 75% OMSW-25% D. salina, keeping a C/N ratio near to 26.7/1.

Assessment of a microalgae pond for post-treatment of the effluent from an anaerobic fixed bed reactor treating distillery wastewater

Abstract An evaluation of the performance of a laboratory‐scale microalgae pond treating effluent from an anaerobic fixed bed reactor digesting distillery wastewater was carried out. The microalgae pond operated with an effluent recycling (R) of 10:1 with respect to the influent and at surface organic loading rates of 418 kg COD ha−1 day−1 and 92 kg BOD5 ha−1 day−1. During the experiment total chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total solids (TS), total suspended solids (TSS), volatile suspended solids (VSS), total nitrogen, ammonia, total phosphorus, orthophosphate, total chlorophyll (C T) and chlorophyll a (C a ) concentrations were monitored. Overall COD and BOD5 removal efficiencies of 98.2 % and 98.8 % were obtained. The global solids removal efficiencies were of 93.2%, 92.6 % and 97.6 % for TS, TSS and VSS, respectively. The removal efficiencies obtained for organic nitrogen and ammonia were 90.2% and 84.1%, respectively. Finally, the removals for total phosphorus and orthophosphate were 85.5% and 87.3%, respectively. It was demonstrated that microalgae grew in this waste by determination of the total chlorophyll and chlorophyll a in the effluent.

Challenges for Cost-Effective Microalgae Anaerobic Digestion

1. Microalgae photosynthesis allows biological CO2 fixation, which is expected to mitigate atmospheric CO2 increase (Amin 2009; Brennan & Owende 2010; Mutanda et al. 2011). 2. Microalgae are 10 – 50 times more efficient than plants in terms of CO2 fixation (Wang et al. 2008). Thus, microalgae can fix 1.83 tonnes of CO2 per 1 tonne of produced microalgae (Chisti 2007). 3. Microalgae can be produced on non-arable areas such as lakes, oceans or deserts, thus reducing competition with food production (Mussgnug et al. 2010; Stephens et al. 2010). This advantage is a key factor when energy supply is considered in desert zones near oceans. 4. Some microalgae can grow under saline conditions, which strengthen the use of micro‐ algae as feedstock for biofuel production in desert zones near the ocean when freshwater supply is not feasible.

Olive Oil Mill Waste Treatment:Improving the Sustainability of the Olive Oil Industry with Anaerobic Digestion Technology

The processes used to treat waste streams are chosen according to technical feasibility, simplicity, economics, societal needs and political priorities. However, the needs and priorities of a sustainable society undergo pressure which means a shift in the focus of wastewater treatment from pollution control to resource exploitation (Angenent et al., 2004). The organic fraction of agro-wastes (e.g. olive oil wastes, sugar beet pulp, potato pulp, potato thick stillage or brewer s grains) has been recognized as a valuable resource that can be converted into useful products via microbially mediated transformations. Organic waste can be treated in various ways, of which bio-processing strategies resulting in the production of bioenergy (methane, hydrogen, electricity) are promising (Khalid et al., 2011). The aim of the present chapter is to discuss: firstly the quantities, characteristics and current treatments of the solid wastes and wastewaters from the continuous olive oil extraction industry for their exploitation and recovery; secondly, anaerobic digestion processes as an alternative for waste treatment and valuable energy recovery

Feasibility of sunflower oil cake degradation with three different anaerobic consortia

Sunflower oil cake (SuOC) is the solid by-product from the sunflower oil extraction process and an important pollutant waste because of its high organic content. For the anaerobic digestion of SuOC three different industrial reactors were compared as inoculum sources. This was done using a biochemical methane production (BMP) test. Inoculum I was a granular biomass from an industrial reactor treating soft-drink wastewaters. Inoculum II was a flocculent biomass from a full-scale reactor treating biosolids generated in an urban wastewater treatment plant. Inoculum III was a granular biomass from an industrial reactor treating brewery wastes. The highest kinetic constant for methane production was achieved using inoculum II. The inoculum sources were analyzed through PCR amplification of 16S rRNA genes and fingerprinting before (t = 0) and after the BMP test (t = 12 days). No significant differences were found in the bacterial community fingerprints between the beginning and the end of the experiments. The bacterial and archaeal communities of inoculum II were further analyzed. The main bacteria found in this inoculum belong to Alphaproteobacteria and Chloroflexi. Of the Archaea detected, Methanomicrobiales and Methanosarcinales made up practically the whole archaeal community. The results showed the importance of selecting an appropriate inoculum in short term processes due to the fact that the major microbial constituents in the initial consortia remained stable throughout anaerobic digestion.