Digestion Of Olive Mill Wastewater Research Articles

Anaerobic Digestion of Olive Mill Wastewater and Process Derivatives—Biomethane Potential, Operation of a Continuous Fixed Bed Digester, and Germination Index

Olive mill wastewater (OMW) management is an economic and environmental challenge for olive oil-producing countries. The recovery of components with high added value, such as antioxidants, is a highly researched approach that could help refinance performant wastewater treatment systems. Anaerobic (co-)digestion is a suitable process to valorize the energetic and nutritional content of OMW and OMW-derived waste streams from resource recovery processes. Issues of process stability, operation, and yields discourage industrial application. Deepening the understanding of biomethane potential, continuous anaerobic digester operational parameters, and co-substrates is key to large-scale implementation. The biomethane potential of different OMW-derived samples and organic solid market waste as co-substrate was 106–350 NL methane per kg volatile solids (VS). The highest yields were obtained with the co-substrate and depolyphenolized OMW mixed with retentate from an ultrafiltration pretreatment. Over 150 days, an anaerobic fixed-bed 300 L digester was operated with different OMW-derived substrates, including OMW with selectively reduced polyphenol concentrations. Different combinations of organic loading rate and hydraulic retention time were set. The biogas yields ranged from 0.97 to 0.99 L of biogas per g of volatile solids (VS) eliminated, with an average methane content in the produced biogas of 64%. Potential inhibition of the process due to high polyphenol concentrations or over-acidification through volatile fatty acids was avoided in the continuous process through process and substrate manipulation. High concentrations of potassium and low concentrations of nitrogen and phosphate end up in the digestate. Sulfate reduction results in high H2S concentrations in the biogas. The digestate was tested for phytotoxic properties via the germination index. Diluted digestate samples improved germination by up to 50%.

Anaerobic Digestion of Olive Mill Wastewater in the Presence of Biochar

Biological treatments focused on stabilizing and detoxifying olive mill wastewater facilitate agronomic reuse for irrigation and fertilization. Anaerobic digestion is particularly attractive in view of energy recovery, but is severely hampered by the microbial toxicity of olive mill wastewater. In this work, the addition of biochar to the digestion mixture was studied to improve the stability and efficiency of the anaerobic process. Kinetics and yields of biogas production were evaluated in batch digestion tests with biochar concentrations ranging from 0 to 45 g L−1. The addition of biochar reduced sensibly the lag phase for methanogenesis and increased the maximum rate of biogas generation. Final yields of hydrogen and methane were not affected. Upon addition of biochar, soluble COD removal increased from 66% up to 84%, and phenolics removal increased from 50% up to 95%. Digestate phytotoxicity, as measured by seed germination tests, was reduced compared to raw wastewater. Addition of biochar further reduced phytotoxicity and, furthermore, a stimulatory effect was observed for a twenty-fold dilution. In conclusion, biochar addition enhances the anaerobic digestion of olive mill wastewaters by effectively reducing methanogenesis inhibition and digestate phytotoxicity, thus improving energy and biomass recovery.

Role of biochar in anaerobic microbiome enrichment and methane production enhancement during olive mill wastewater biomethanization.

The current research work attempted to investigate, for the first time, the impact of biochar addition, on anaerobic digestion of olive mill wastewater with different initial chemical oxygen demand loads in batch cultures (10g/L, 15g/L, and 20g/L). Methane yields were compared by applying one-way analysis of variance (ANOVA) followed by post-hoc Tukey's analysis. The results demonstrated that adding at 5g/L biochar to olive mill wastewater with an initial chemical oxygen demand load of 20g/L increased methane yield by 97.8% and mitigated volatile fatty acid accumulation compared to the control batch. According to the results of microbial community succession revealed by the Illumina amplicon sequencing, biochar supplementation significantly increased diversity of the microbial community and improved the abundance of potential genera involved in direct interspecies electron transfer, including Methanothrix and Methanosarcina. Consequently, biochar can be a promising alternative in terms of the recovery of metabolic activity during anaerobic digestion of olive mill wastewater at a large scale.

Thermophilic anaerobic digestion of olive mill wastewater in an upflow packed bed reactor: Evaluation of 16S rRNA amplicon sequencing for microbial analysis

Olive mill wastewater, a by-product of olive oil production after the operation of three-phase decanters, was used in a thermophilic anaerobic digester targeting efficient bioconversion of its organic load into biogas. An active anaerobic inoculum originating from a mesophilic reactor, was acclimatized under thermophilic conditions and was filled into a high-rate upflow packed bed reactor. Its performance was tested towards the treatment efficacy of olive mill wastewater under thermophilic conditions reaching the minimum hydraulic retention time of 4.2 d with promising results. As analysis of the microbial communities is considered to be the key for the development of anaerobic digestion optimization techniques, the present work focused on characterizing the microbial community and its variation during the reactor's runs, via 16S rRNA amplicon sequencing. Identification of new microbial species and taxonomic groups determination is of paramount importance as these representatives determine the bioprocess outcome. The current study results may contribute to further olive mill wastewater exploitation as a potential source for efficient biogas production.

Bio-fertilizers issued from anaerobic digestion for growing tomatoes under irrigation by treated wastewater: targeting circular economy concept

Tomatoes (Solanum lycopersicum) plant were provided with bio-fertilizers issued from anaerobic digestion of olive mill wastewater without and with 1%, 5% of phosphate residues in mesophilic conditions for 25 days. 1% of raw substrates (OMW raw; OMW + 1%PR raw; olive mill wastewater + 5%phosphate residues raw; and phosphate residues) and digestates (olive mill wastewater digestate, olive mill wastewater + 1%phosphate residues digestate and olive mill wastewater + 5%phosphate residues digestate) was provided fortnightly to the plants. Reclaimed water from a wastewater treatment plant located in the study site was used for automatically controlled irrigation. It contained a low level of chemical fertilizers to compare tomato plant growth, leaf analysis, steam water potential, production yield and fruit quality results to plants fed with bio-fertilizers. Generally, parameters and results were progressively increased during the growing and harvesting stage, which refer to the essential elements that cover the plant’s needs. Plants fed with bio-fertilizers showed the most extended plant height (olive mill wastewater + 5% phosphate residues raw), and the best accumulation of essential elements in leaves (olive mill wastewater + 1% phosphate residues digestate and olive mill wastewater + 5%phosphate residues digestate). The maximum average fruit weight per treatment (35.5 g) was obtained when applying the digestates mixture of olive mill wastewater raw and olive mill wastewater + 5% phosphate residues. The maximum yield production per plant was obtained when applying phosphates residues. Bio-fertilizers (digestates) showed good performances, high fruit quality and perfect tomato yield production compared to the control plants. Results obtained during this study are considered promising regarding environmental framework. However, this study was done in a laboratory scale and needs to be applied in a large scale to provide more data on the effectiveness of the digestates application. It is also recommended to apply these bio-fertilizers on different crops and various soils for a better evaluation.

Effect of mixture ratio and organic loading rate during anaerobic co-digestion of olive mill wastewater and agro-industrial wastes

Environmental pollution is a serious concern within the Mediterranean area, this situation results mainly from olive mill wastewaters (OMW), the liquid effluents generated during olive oil extraction. Anaerobic digestion of olive mill wastewaters is negatively affected by nitrogen deficiency, low pH, and the presence of phenolic compounds. This study examines the feasibility of OMW co-digestion with rich nitrogen substrates in batch and continuous mode under mesophilic conditions. Four substrates were tested at different ratios (substrate/OMW) in batch mode. Optimal ratio (substrate/OMW) was 80:20 for poultry manure (PM), 20:80 for both cheese whey (CW) and grass, and 50:50 for slaughterhouse wastewater (SWW). Furthermore, the effect of organic loading rate was assessed in continuous mode, using an anaerobic sequencing batch reactor for the mix (SWW/OMW) at 50:50. The reactor was able to degrade 10 g COD/L/day, as the maximal limit for biogas production and process stability. The results proved that co-digestion of SWW with OMW at 50:50 produced the higher biogas volume in batch mode and ensure good process stability, expressed by high alkalinity (2150 eq mg CaCo3/L) and low rate of volatile fatty acids (VFA) (150 eq mg acetic acid/L). Co-digestion of OMW with SWW is an efficient solution, to solve environmental pollution and recover renewable energy from these two organic wastes.

Performance and microbial analysis during long‐term anaerobic digestion of olive mill wastewater in a packed‐bed biofilm reactor

AbstractBACKGROUNDThe treatment of olive mill wastewater (OMWW) in a packed bed biofilm reactor (PBBR) and the identification of different microorganisms involved in the digestion process is an attractive field for research.RESULTSA PBBR treating OMWW under different organic loading rates (OLRs) (0.94–9.36 gCOD/(L d)), showed high stability during an extensive time (723 days) without any sign of acidification. High volumetric biogas and methane (CH4) productions, 4.1 and 2.4 LN/(Lreactor d), respectively were registered at the highest OLR. Meanwhile, high chemical oxygen demand (COD) removal (62.5–79.7%) was obtained throughout the experiment. Phenolic compounds removal was much higher during the first steps of the experiment (75.9–84.2%), and decreased as the OLR increased to about 38%. High homogeneity of biofilm thickness and Bacteria and extracellular polymeric substance distribution were demonstrated by confocal laser scanning microscopy. Results of real‐time quantitative polymerase chain reaction (PCR) and 16S rRNA amplicon analyses showed that Bacteria, mainly consisting of Firmicutes, Proteobacteria, Bacteroidetes and Chloroflexi phylum, was about eight times more abundant than Archaea in the reactor liquid phase, while Bacteria to Archaea ratio was almost one in the biofilm. This points to a major degradation of organic substances in the liquid, while methanogenesis occurred mainly within the biofilm. In the liquid, acetoclastic methanogens were more abundant than hydrogenotrophic ones, while both groups showed likely very similar contributions in the biofilm.CONCLUSIONPromising results have been presented throughout this work providing information about the long‐term operation of PBBR‐granular activated carbon treating OMWW and analyzing, in an efficient manner, the structure and the composition of the microbial community involved in OMWW digestion. © 2019 Society of Chemical Industry

Packed-bed biofilm reactor for semi-continuous anaerobic digestion of olive mill wastewater: performances and COD mass balance analysis

ABSTRACT In the present study, the treatability of olive mill wastewater (OMWW) using an anaerobic fixed bed biofilm reactor packed with granular activated carbon (GAC) and inoculated with non-acclimated biomass was performed in a semi-continuous mode under mesophilic conditions. Three organic loading rates (OLR) varied from 0.94 to 2.81 g COD/(L d) were applied. The results of batch adsorption tests on GAC and the experimental data from PBBR-GAC operation were used to set up a COD mass balance in order to investigate the effect of adsorption on the COD removal during the three anaerobic treatment steps. Despite the slight accumulation of volatile fatty acids (VFAs) during the second and the third steps, between 735 and 1135 mg COD/L (as acetic acid), a stable environment for methanogens was maintained for a period of 104 days. During the three steps, degradation levels were up to 80% of COD and 85% of phenolic compounds. An averaged specific biogas production of 1.77 LN/d and a methane (CH4) concentration of about 60%, corresponding to a CH4 yield of 0.31 L CH4produced/g CODdepleted, were reached at an OLR of 2.81 g COD/(L d). The results show that the COD mass balance was not closed during the first two steps, while in the third step, it could be around 96%. This finding suggests that the adsorption of organic substances on activated carbon occur just during the two first steps, while at 2.81 g COD/(L d) OLR no adsorption is occurring and the introduced COD becomes completely available for CH4 production.

Anaerobic Digestion of Olive Mill Wastewater: Focusing on the Effect of Nitrogen Source

Anaerobic Digestion of Olive Mill Wastewater: Focusing on the Effect of Nitrogen Source

Limiting factors for anaerobic digestion of olive mill wastewater blends under mesophilic and thermophilic conditions

Experimental trials of anaerobic digestion of olive mill wastewater (OMW) blended with other agro-industrial by-products were carried out to evaluate biogas production and sensitivity of the process to inhibiting compounds. Blends containing different percentages of OMW, digested liquid manure, and citrus peel were subjected to a batch anaerobic digestion process under both mesophilic and thermophilic conditions. The results showed that blends with percentages of OMW higher than 20% (v/v) had low methane yields due high concentrations of polyphenols (PPs) and/or volatile fatty acids (concentrations above 0.8 g kg–1 and 2.4 g L–1, respectively). The addition of other substrates such as citrus peel may have induced synergic inhibiting effects of PPs and essential oils (EO) on microbial growth. Thermophilic processes were more sensitive to these inhibiting compounds than mesophilic processes. The results of this study suggest that reducing PPs and EO concentrations in blends subject to anaerobic digestion below the inhibiting concentrations of 0.6 g L–1 and 0.5 g kg–1, respectively, is suitable. Additionally, it is advisable to maintain the volatile fatty acids content below 2 g L–1 to avoid its evident toxic effects on the growth of microorganisms in biochemical processes.

Effect of Fenton pretreatment on anaerobic digestion of olive mill wastewater and olive mill solid waste in mesophilic conditions

ABSTRACTThe olive mill waste (OMW) generated from olive oil extraction process constitutes a major environmental concern owing to its high organic and mineral matters and acidic pH. Anaerobic digestion (AD) is a main treatment for reducing the organic matter and toxic substances contained in OMW and generating at the same time, energy in the form of biogas. AD of OMW that contains lignocellulose is limited by the rate of hydrolysis due to their recalcitrant structure. This study is devoted to the effect of Fenton process (FP) pretreatment on olive mill wastewater (OMSW) /olive mill solid waste (OMWW) co-digestion to improve their digestibility and in this way the biogas production. The FP pretreatment was performed in batch mode at 25°C, various H2O2/[Fe2+] ratios (100–1200), catalyst concentration ([Fe2+]) ranging from 0.25 to 2 mM, reaction time varying from 30 to150 min, and different pH (3–11). The best performance was obtained with H2O2/[Fe2+] = 1000, [Fe2+] = 1.5 mM, 120 min, and pH 3. Biochemical methane potential (BMP) tests conducted in batch wise digester and at mesophilic conditions (37 °C) showed that cumulative biogas and methane production were higher without FP treatment, and correspond to 699 and 416 mL/g VS, respectively. However, pre-treated OMSW results into an increase of 24% of methane yield. After 30 days of AD, the methane yield was 63%, 54%, and 48%, respectively, for OMSW treated without iron precipitation, with iron precipitation and untreated OMSW sample.

Effect of aerobic pretreatment on anaerobic digestion of olive mill wastewater (OMWW): An ecoefficient treatment

Anaerobic digestion experiments of olive mill wastewater (OMWW) without pretreatment were carried out and signs of inhibition in the biological process were observed after a time equal to 1.5 times the Hydraulic Residence Time (HRT) due to the presence of a high inhibitors concentration in OMWW. Based on these findings, OMWW was subjected to an aerobic pretreatment in order to reduce the concentration of phenolic compounds and decrease Total Chemical Oxygen Demand (TCOD), achieving a reduction of 78% and 90% of the initial polyphenols concentration and 18% and 21% TCOD reduction when the substrate was aerated for 5 and 7 days respectively.Finally, anaerobic digestion experiments using OMWW aerated for 5 and 7 days as substrate were conducted to determine the influence of aeration time on methane yields and TCOD reduction. The results yield 5 days as the aeration time that achieves best results, given that this stabilizes the anaerobic process, can reduce the TCOD by 65% and generates almost 0.39m3 methane/kg removed TCOD.Anaerobic digestion of OMWW will be economically feasible if the waste is pretreated by aerobic digestion, since the period of return of investment obtained under these conditions does not exceed 6 years.

Anaerobic digestion of olive mill wastewater

Anaerobic digestion of olive-mill wastewater (OMW) was carried out in a continuously fed mode bioreactor. The bioreactor was operated at different hydraulic retention times (HRTs), using OMW, either raw or pre-treated with white-rot fungi. Two different kinds of feed were tested in this process, one which was thermally treated and subjected to sedimentation, in order to remove the solids contained and the other without any physicochemical treatment (raw OMW). Thermally pretreated OMW did not allow a stable operation even at an HRT of 30d. Further pretreatment of the OMW with a white-rot fungus for removal of the contained phenolics, allowed a stable operation at an HRT of 30 d. On the other hand, simple dilution of the raw wastewater, without any solids removal, lead to a stable operation at an HRT of 30d and was accompanied by higher production of biogas. The presence of the solids in the OMW proved to be a determining factor for the stability of the process and could be attributed to a possible adsorption on the solids of hydrophobic compounds, such as long-chain fatty acids that are toxic to methanogens.

Anaerobic acidogenic digestion of olive mill wastewaters in biofilm reactors packed with ceramic filters or granular activated carbon

Four identically configured anaerobic packed bed biofilm reactors were developed and employed in the continuous acidogenic digestion of olive mill wastewaters to produce volatile fatty acids (VFAs), which can be exploited in the biotechnological production of polyhydroxyalkanoates. Ceramic porous cubes or granular activated carbon were used as biofilm supports. Aside packing material, the role of temperature and organic loading rate (OLR) on VFA production yield and mixture composition were also studied. The process was monitored through a chemical, microbiological and molecular biology integrated procedure. The highest wastewater acidification yield was achieved with the ceramic-based technology at 25 °C, with an inlet COD and an OLR of about 17 g/L and 13 g/L/day, respectively. Under these conditions, about the 66% of the influent COD (not including its VFA content) was converted into VFAs, whose final amount represented more than 82% of the influent COD. In particular, acetic, propionic and butyric acids were the main VFAs by composing the 55.7, 21.5 and 14.4%, respectively, of the whole VFA mixture. Importantly, the relative concentrations of acetate and propionate were affected by the OLR parameter. The nature of the packing material remarkable influenced the process performances, by greatly affecting the biofilm bacterial community structure. In particular, ceramic cubes favoured the immobilization of Firmicutes of the genera Bacillus, Paenibacillus and Clostridium, which were probably involved in the VFA producing process.

Anaerobic digestion of olive mill wastewater in a periodic anaerobic baffled reactor (PABR) followed by further effluent purification via membrane separation technologies

AbstractBACKGROUND: The combined treatment of olive mill wastewater (OMWW) by applying the anaerobic digestion process and further treatment in a system consisting of filters and membranes is presented. The anaerobic digestion of the OMWW took place in a high rate system, the periodic anaerobic baffled reactor (PABR). Application of the membrane system aimed at purifying the anaerobic effluent.RESULTS: An increase in the organic loading rate was achieved by increasing the influent chemical oxygen demand (COD) and alternatively by decreasing the hydraulic retention time (HRT). The first option caused process failure, since the volatile fatty acids accumulation resulted in negligible biogas production. In contrast, the second change (decrease in HRT) led to stable operation that permitted the reduction of the HRT to 3.75 d and increase of the organic loading rate to 8.9 g tCOD L−1 d−1 with satisfactory total COD removal (72%). Higher total COD removal (up to 80%) was observed at lower organic loading rates (<3.5 g tCOD L−1 d−1). Further purification in the membrane units resulted in a final permeate of less than 0.1 g tCOD L−1. The membrane systems proved to be more efficient on the anaerobic effluent than on the raw OMWW (the final permeate in that case contained 1g tCOD L−1).CONCLUSIONS: The anaerobic digestion of OMWW in a PABR was stable even at high organic loading rates. Filtering and membrane fractionation of the PABR effluent resulted in a final permeate stream of high quality, suitable for irrigation and/or reuse in the proposed operating scheme for diluting the OMWW prior to anaerobic digestion. Copyright © 2009 Society of Chemical Industry

Response of methanogen populations to organic load increase during anaerobic digestion of olive mill wastewater

AbstractProcess performances of an upflow anaerobic filter treating olive mill wastewater and the response of methanogenic Archaea to increasing volumetric organic load (VOL) were studied. At a VOL of 15 g chemical oxygen demand (COD) L−1 day−1, 90% of the influent COD was removed. Following a VOL increase from 6 to 15 g COD L−1 day−1, the polymerase chain reaction (PCR) titre of hydrogenotrophic Methanobacterium, determined by magnetic capture of the target DNA and group‐specific PCR based on the 16S rRNA gene, decreased from 1011 to 108 cells g−1 sludge, while that of Methanomicrobiaceae and relatives increased from 104 to 106 cells g−1 sludge. Methanosaeta‐like acetoclastic methanogens were less affected by VOL variation and dominated at high VOL with a 16S rRNA gene PCR titre of 109 cells g−1 sludge. Single‐strand conformation polymorphism analysis of the PCR‐amplified archaeal 16S rRNA gene showed a stable band pattern, indicating that VOL variation affected the methanogen PCR titre but not the archaeal community structure. Copyright © 2006 Society of Chemical Industry

Anaerobic digestion of olive mill wastewaters in biofilm reactors packed with granular activated carbon and “Manville” silica beads

Anaerobic digestion is one of the most promising technologies for disposing olive mill wastewaters (OMWs). The process is generally carried out in the conventional contact bioreactors, which however are often unable to efficiently remove OMW phenolic compounds, that therefore occur in the effluents. The possibility of mitigating this problem by employing an anaerobic OMW-digesting microbial consortium passively immobilized in column reactors packed with granular activated carbon (GAC) or “Manville” silica beads (SB) was here investigated. Under batch conditions, both GAC- and SB-packed-bed biofilm reactors exhibited OMW COD and phenolic compound removal efficiencies markedly higher (from 60% to 250%) than those attained in a parallel anaerobic dispersed growth reactor developed with the same inoculum; GAC-reactor exhibited COD and phenolic compound depletion yields higher by 62% and 78%, respectively, than those achieved with the identically configured SB-biofilm reactor. Both biofilm reactors also mediated an extensive OMW remediation under continuous conditions, where GAC-reactor was much more effective than the corresponding SB-one, and showed a tolerance to high and variable organic loads along with a volumetric productivity in terms of COD and phenolic compound removal significantly higher than those averagely displayed by most of the conventional and packed-bed laboratory-scale reactors previously proposed for the OMW digestion.

Performances and microbial features of a granular activated carbon packed-bed biofilm reactor capable of an efficient anaerobic digestion of olive mill wastewaters

Anaerobic digestion of olive mill wastewaters is generally performed in anaerobic contact bioreactors where the removal of toxic phenols is often unsatisfactory. In the present work we show that a granular activated carbon packed-bed biofilm reactor can be successfully used to achieve effective and reproducible wastewater decontamination even at high organic loads. A comparison of 16S rRNA gene sequences of the inoculum and of biomass samples from different districts of the reactor revealed enrichment of specific microbial populations, probably minor members of the inoculum and/or of the olive mill wastewaters. They mainly consisted of the members of Proteobacteria, Flexibacter-Cytophaga-Bacteroides, and sulphate-reducing bacteria. The dominant sequence among Archaea (70% of clones) was closely related to Methanobacterium formicicum.

Performances and microbial features of a granular activated carbon packed-bed biofilm reactor capable of an efficient anaerobic digestion of olive mill wastewaters

Anaerobic digestion of olive mill wastewaters is generally performed in anaerobic contact bioreactors where the removal of toxic phenols is often unsatisfactory. In the present work we show that a granular activated carbon packed-bed biofilm reactor can be successfully used to achieve effective and reproducible wastewater decontamination even at high organic loads. A comparison of 16S rRNA gene sequences of the inoculum and of biomass samples from different districts of the reactor revealed enrichment of specific microbial populations, probably minor members of the inoculum and/or of the olive mill wastewaters. They mainly consisted of the members of Proteobacteria, Flexibacter-Cytophaga-Bacteroides, and sulphate-reducing bacteria. The dominant sequence among Archaea (70% of clones) was closely related to Methanobacterium formicicum.

Evaluating process imbalance of anaerobic digestion of olive mill wastewaters

Process control measures are of critical importance which guard against process instability of anaerobic digestion. By introducing perturbations in an up-flow anaerobic filter reactor fed with olive mill wastewaters (OMWs), reliable parameters that could suggest process imbalance were determined. The reactor was operated for a period of 10 days at 37 °C and at an HRT of 23 days corresponding to a loading rate of 0.75 g COD l−1 per day. Changing the organic loading rate (OLR), hydraulic retention time (HRT) and temperature lead to reactor performance failure. A decrease in biogas production and methane yield was observed together with an accumulation of VFAs such as acetate, propionate, butyrate, isobutyrate, and valerate. Significant concentrations of butyrate, isobutyrate, and valerate accumulated when acetate and propionate concentrations were very high. The pH at the bottom of the reactor, where substrates were introduced, showed a low pH value (acid), whereas no such change was observed at the top of the reactor. Valerate accumulation was shown to be the most toxic of all VFAs but an accumulation of propionate, butyrate and acetate also inhibited the functioning of the reactor.