Toxic effect of coloured olive compounds on the anaerobic digestion of olive oil mill effluent in UASB-like reactors

Anaerobic sludge digestion of olive oil mill effluent (OOME) in Upflow Anaerobic Sludge Blanket (UASB) reactors was shown to be unstable as a result of both chemical and biological parameters. The study was complicated by the fact that Chemical Oxygen Demand (COD) was removed by growth and maintenance of active biomass and by adsorption in and on the sludge. Coloured compounds caused an inhibition effect on the anaerobic digestion of the wastewater. This inhibition, shown at low COD concentrations of diluted OOME, was due to accumulation of recalcitrant coloured compounds in the sludge, inducing irreversible inhibition of bacterial growth. Partial decolourization of OOME through resin (Duolite XAD 761) treatment reduced the toxic effect.     

Anaerobic digestion of alkaline black liquor using an up-flow anaerobic sludge blanket reactor

The anaerobic digestion of alkaline black liquor from a cereal straw pulping mill was studied in batch (serum bottles) and continuous systems (up-flow anaerobic sludge blanket reactor—UASB). The batch digestion studies confirmed that lignin and related compounds (LRC) in the alkaline black liquor were the main inhibitory substances and could not be decomposed by anaerobic bacteria. At organic loading rates of 5–10 kg COD m^?3 day^?1, the UASB reactor achieved 50–60% COD removal efficiencies. Gas production was 2–3 dm³ per dm³ of alkaline black liquor. Two different sludge types were examined in the reactor: granular and cluster-like sludges. Sludge in a cluster, which involved many small granules and flocs, tended to form larger aggregates and possessed good settling ability.     

Isolation of a yeast,Trichosporon cutaneum,able to use low molecular weight phenolic compounds: application to olive mill waste water treatment

This study deals with the degradation of phenolic compounds in olive oil mill waste; a highly polluting material in olive oil‐producing countries because of its abundance and the toxicity of its phenolic compound content. This investigation confirms the ability of an isolated yeast, identified as Trichosporon cutaneum, to degrade phenolic compounds extracted from olive mill waste water (OMW). The yeast was adapted to the OMW by an enrichment culture. The results of this biotransformation were a decrease in the phenolic content and hence a reduction in the phytotoxic effects of the effluent after the yeast treatment. The kinetic growth of the isolated yeast on phenol over a range of concentrations (0.3–3.0 g dm^?3) was studied. The ability of the strain to assimilate simple monomeric phenols and alkyl phenols, at a concentration of 1 g dm^?3, in a synthetic liquid medium used as the sole carbon source was investigated in a batch culture. The aromatic ring cleavage pathway occurred in the yeast through catechol oxidation. Using various concentrations of ethyl acetate extract from OMW as the sole carbon source, the yeast exhibited growth on the substrate up to 7 g dm^?3 equivalent of phenols. A significant reduction of COD after the treatment of the OMW extract by the yeast isolate was noticed. The removal of phenol and COD exceeded 80% of the original loading after 8 days of treatment, for extracts containing initial COD in the range 19 to 72 g dm^?3. Copyright © 2004 Society of Chemical Industry     

Effect of coagulation on palm oil mill effluent and subsequent treatment of coagulated sludge by anaerobic digestion

A new effluent treatment scheme is proposed for treating palm oil mill effluent based on coagulation and anaerobic digestion of coagulated sludge. The effectiveness of anionic (N9901) and cationic (N9907) polyelectrolytes manufactured by NALCO (Malaysia) was evaluated both as coagulant and coagulant aid. The results showed that the anionic and cationic polyelectrolytes were best suited as a coagulant aid, and the cationic polyelectrolyte showed better performance than the anionic polyelectrolyte. For an influent chemical oxygen demand (COD) concentration of 59 700 mg L^?1 at an alum dosage of 1700 mg L^?1, the residual COD, suspended solid removal, sludge volume and pH were found to be 39 665 mg L^?1, 87%, 260 mL L^?1 and 6.3, respectively. For the above influent COD and alum dosage with the addition of 2 mg L^?1 of cationic polyelectrolyte as coagulant aid, the results were 30 870 mg L^?1, 90%, 240 mL L^?1 and 6.2, respectively. The sludge resulting from the coagulation process using alum as coagulant and cationic polyelectrolyte as coagulant aid was tested for its digestibility in an anaerobic digester. The quantity of biogas generated per gram of volatile solids (VS) destroyed at a loading rate of 26.7 ± 0.5 and 35.2 ± 0.4 g VS L^?1 d^?1 was found to be 0.68 and 0.72 L g^?1 VS destroyed. The anaerobic biomass when subjected to varying alum dosage in the coagulated palm oil sludge did not exhibit inhibition as the digester performance was in conformity with the regular treatment process Copyright © 2006 Society of Chemical Industry     

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

BACKGROUND: 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     

Anaerobic digestion of Aegean olive mill effluents with and without pretreatment

BACKGROUND: Olive oil production is an important economical activity in the Aegean region of Turkey. However, the effluents of the olive oil producing mills with their high organic loads and toxic compounds are causing serious environmental problems. The anaerobic biological treatment of olive mill wastewater (OMWW) using the treatment plants of the regional industries could be a method of choice and within the scope of this study floccular and granular sludges were investigated in batch mode for their success in the treatment of OMWW while producing biogas. The major limitation of this treatment is the inhibition of methanogenic bacteria by the phenolic compounds in OMWW. Thus an integrated solution was suggested in which a pre‐treatment step (dephenolization) was also introduced before biological step. RESULTS: The effluents of 27 olive mills out of 47 were found to have total phenolics (TP) less than 3 g L^?1 and could be treated anaerobically after simple dilution. The biogas production for the untreated OMWW was higher for floccular sludge than for the granular sludge (68.5 mL and 45.7 mL respectively). Combined pre‐treatment experiments, first coagulation with polyaluminum chloride, followed by flocculation with cationic polyelectrolyte and finally Fenton's oxidation, could remove 80% of TP and 95% of the total suspended solids. CONCLUSION: OMWW having TP values less than 3 g L^?1 can be treated anaerobically using floccular sludge after simple dilution and biogas can be produced. For OMWW samples having higher TP values pre‐treatment is necessary and the pre‐treatment given in this study may be used effectively. Copyright © 2010 Society of Chemical Industry     

A comparison of treatment methods for palm oil mill effluent (POME) wastes

A study of the operational variables involved in the treatment of palm oil mill effluent (POME) was carried out. These included the acidic or alkaline nature of the POME discharged from the oil mills, the efficiency of the decay (or digestion) of the chemical oxygen demand (COD) contents of the POME, the economic benefits that could arise from the digested sludge and biogas and finally the net economic recovery abilities of the various treatment methods available. The chemical oxygen demand (COD) contents of the POME must be reduced to an acceptable level of 2000–3000 mg solids dm^?3 of sludge before the latter can be used as a fertiliser material. In 10 days of operational periods various anaerobic digestion treatment methods gave COD reduction efficiencies of 76–96%, the batch pond anaerobic digestion mode gave an efficiency of 76.5%, the continuous pond modes 92.5–95.5% and the tank digester 93.8%. In all anaerobic operations the optimal pH values of the POME media were in the range 7.1–7.6 and a ratio of the volatile acids to the total alkalinity of the media (VA/TA) of 0.3 or less was found to enhance the performance of these digesters. Economic analyses carried out on all modes of treatment gave the following economic recovery abilities: the decanter/drier system gave a break-even situation of 3 years, the tank digester system, 2 years, and the single stage anaerobic pond system, 6 years. The batch pond system appeared not to give a break-even situation. Of the treatment methods examined the decanter/drier and tank digester systems were concluded to be optimal.     

Decolorization of olive oil mill effluent by physical and chemical treatment prior to anaerobic digestion

Chemical and physical treatment of olive oil mill effluent (OOME) was performed using iron and lime as complexing agents, Duolite XAD 761 resin as phenolic adsorbent and hydrogen peroxide as oxidant. We have shown that 10 g dm⁻³ of ammonium iron(III) sulphate·12H₂O, or calcium dihydroxide were sufficient to precipitate more than 50% of the initial COD and remove 50% of the initial colour within a short contacting time. The aromatic adsorbent resin retained more than 50% of the colouring compounds (chromophores) corresponding to removal of more than 60% of the initial COD after treating three bed volumes of crude OOME. The efficiency depended on the volume treated. Hydrogen peroxide removed the substituents of the aromatic rings which resulted in a decrease in length of the colouring compounds in OOME. However, they were not completely degraded, leading to shorter wavelength absorption. This chemical treatment was efficient in colour removal but only 19% COD removal was possible. In all cases, simple aromatics were reduced, as determined by GPC analysis. The chemical and physical decolorization of OOME was efficient in reducing the toxic effect of recalcitrant compounds. The resultant OOME by each of these alternative treatments was readily degradable through anaerobic digestion. © 1998 Society of Chemical Industry     

Kinetic study of an anaerobic fluidized bed system used for the purification of fermented olive mill wastewater

The anaerobic digestion of olive mill wastewater (OMW) in a fluidized bed, pretreated with Geotrichum candidum, has been studied. The bioreactor used (volume = 3.5 dm³; biomass concentration = 11.5 g VSS dm^?3) maintained satisfactory operation for 4 to 35 days, in terms of hydraulic retention time, and removed 92% of the initial COD. The system was used to develop and test a kinetic model which was subsequently employed to determine growth yield and maintenance coefficient. From the results obtained, the Michaelis-Menten equation accurately described the substrate uptake (i.e. COD removal) in the anaerobic fluidized bed system. Pretreatment of the OMW was found to increase the rate of substrate uptake by a factor of 3.2 when compared to untreated OMW.     

The methanogenic toxicity of wastewater lignins and lignin related compounds

Lignin derivatives are major components of wastewater streams generated in the chemical processing of wood. The objective of this study was to evaluate the inhibitory effect of various lignins isolated from forest industry wastewaters, and selected lignin model compounds, on methanogenic bacteria. The methanogenic inhibition was determined at 30°C in standard toxicity assays, utilizing anaerobic granular sludge as inoculum. The wastewater lignins differed considerably in their inhibitory activity. Some lignin samples were nontoxic, whereas others caused 50% inhibition at concentrations ranging from 3320 to 5950 mg COD dm^?3. Experiments with ultrafiltered lignins revealed that the toxicity of the inhibitory lignin samples originated from the low molecular weight fraction. In additional studies with low molecular weight lignin model compounds, it was observed that the inhibitory activity of these compounds was related to the functional groups on the aromatic ring. Compounds with aldehyde groups or apolar substituents were highly toxic, whereas those with carboxylic groups only caused significant inhibition at high concentrations. These results indicate that low molecular weight lignin derivatives in forest industry wastewaters are potential inhibitors of anaerobic treatment systems.     

Olive Mill and Winery Wastewaters Pre-Treatment by Coagulation with Chitosan

The pre-treatment of both winery wastewater (WW) and olive mill wastewater (OMW) by coagulation, using a natural organic coagulant, was investigated as a possible alternative to conventional metal based coagulants, in order to produce a potentially reusable organic sludge. Chitosan was chosen as a model natural organic coagulant and the coagulation process was optimized investigating different coagulant doses and pH values. In spite of the notably lower polluting load for the WW compared to the OMW, the efficiency of the chitosan coagulation was found to be high in terms of total suspended solids (81% and 80% for OMW and WW respectively) and turbidity (94% and 92% for OMW and WW respectively) removal for both wastewaters, but a notable difference was observed in terms of organic matter removal (32% and 73% in terms of COD for OMW and WW respectively). Taking into account that the best performances of the coagulation process by chitosan were achieved at the actual pH for OMW as well as no significant differences were observed for WW as the pH was changed, no chemicals addition is required to adjust pH.     

含油废水处理厂污泥的厌氧消化试验

为研究含油废水处理产生的剩余污泥和气浮污泥的厌氧消化性能,试验采取序批式厌氧消化两种含油污泥的方法,对含油污泥的组成变化及产气性能进行测定,并将其结果与市政剩余污泥进行对比。试验结果显示,经过35天的厌氧消化,含油剩余污泥和含油气浮污泥的可挥发固体（VS）降解率分别为4.98%和3.74%,TCOD降解率分别为10%和3.4%,产气量分别为0.97 L/gVS和0.56 L/gVS。经过和市政剩余污泥对比后表明,含油气浮污泥厌氧消化性能差,不宜进行厌氧消化处理;含油剩余污泥厌氧消化性能相对强于含油气浮污泥,但弱于市政剩余污泥。     

The effect of organic loading rate on the anaerobic digestion of two‐phase olive mill solid residue derived from fruits with low ripening index

A study of the effect of organic loading rate on the performance of anaerobic digestion of two‐phase olive mill solid residue (OMSR) was carried out in a laboratory‐scale completely stirred tank reactor. The reactor was operated at an influent substrate concentration of 162 g chemical oxygen demand (COD) dm^?3. The organic loading rate (OLR) varied between 0.8 and 11.0 g COD dm^?3 d^?1. COD removal efficiency decreased from 97.0% to 82.6% when the OLR increased from 0.8 to 8.3 g COD dm^?3 d^?1. It was found that OLRs higher than 9.2 g COD dm^?3 d^?1 favoured process failure, decreasing pH, COD removal efficiency and methane production rates (Q_M). Empirical equations described the effect of OLR on the process stability and the effect of soluble organic matter concentration on the total volatile fatty acids (TVFA)/total alkalinity (TAlk) ratio (ρ). The results obtained demonstrated that rates of substrate uptake were correlated with concentration of biodegradable COD, through an equation of the Michaelis–Menten type. The kinetic equation obtained was used to simulate the anaerobic digestion process of this residue and to obtain the theoretical COD degradation rates in the reactor. The small deviations obtained (equal to or lower than 10%) between values calculated through the model and experimental values suggest that the proposed model predicts the behaviour of the reactor accurately. Copyright © 2007 Society of Chemical Industry     

Combined Ozone Pretreatment and Anaerobic Digestion for the Reduction of Biological Sludge Production in Wastewater Treatment

The ever-increasing amount of solid waste generated by wastewater treatment plants highlights emerging economic and environmental issues. In order to develop new processes producing less sludge, the use of ozone combined with anaerobic digestion was investigated for waste activated sludge treatment. This paper was aimed at evaluating the impact of ozone pretreatment on anaerobic digestion and particularly the enhancement of biogas production. Sludge solubilization was estimated in terms of modification of chemical oxygen demand, solids and nitrogen. Batch anaerobic digestion highlighted the enhancement of ozonated sludge biodegradability. Ozonation led to an increase in biogas production. The ozone dose of 0.15 g O₃/g total solids resulted in a considerable increase in the soluble COD ratio from 4% to 37%. This ozone dose achieved the highest increase in biogas production: 2.4 times greater than without chemical pretreatment.     

Anaerobic biogas generation from sugar industry wastewaters in three‐phase fluidized‐bed bioreactor

In the present study, attempts are made to optimize digestion time, initial feed pH, feed temperature, and feed flow rate (organic loading rate, OLR) for maximum yield of methane gas and maximum removal of chemical oxygen demand (COD) and biological oxygen demand (BOD) of sugar industry wastewaters in three‐phase fluidized‐bed bioreactor. Methane gas is analysed by using flame‐ionisation detector (FID). The optimum digestion time is 8 h and optimum initial pH of feed is observed as 7.5. The optimum temperature of feed is 40°C and optimum feed flow rate is 14 L/min with OLR 39.513 kg COD/m³ h. OLR is calculated on the basis of COD inlet in the bioreactor at different flow rates. The maximum methane gas concentration is 61.56% (v/v) of the total biogas generation at optimum biomethanation process parameters. The maximum biogas yield rate is 0.835 m³/kg COD/m³ h with maximum methane gas yield rate (61.56%, v/v) of 0.503 m³/kg COD/m³ h at optimum parameters. The maximum COD and BOD reduction of the sugar industry wastewaters are 76.82% (w/w) and 81.65% (w/w) at optimum biomethanation parameters, respectively.     

Recovery of Natural Antioxidants from Olive Mill Wastewater Using Genapol-X080

The possibility of applying cloud point extraction (CPE) using Genapol X-080 as surfactant for the separation of phenolic compounds from olive mill wastewater was examined. The ability of the surfactant to recover individual and mixtures of polyphenols and tocopherols in various concentrations from aqueous solutions was tested before its application for the recovery of phenols from olive mill wastewater. Many of the examined individual polyphenols were recovered at high percentage. Especially, in the case of Luteolin, low surfactant concentrations were sufficient for quantitative removal. The recovery appeared proportional to the surfactant concentration. The complete recovery of tocopherols was also possible. Total phenol recovery by simple and successive CPE of olive mill wastewater with various concentrations (2, 5 and 20%, v/v) of Genapol X-080 was up to 89.5%.     

Ozonation as a Pre-treatment for Anaerobic Digestion of Waste-Activated Sludge: Effect of the Ozone Doses

The aim of the present study was to improve the anaerobic biodegradability of waste-activated sludge by using ozonation. The effect of different ozone doses was assessed in terms of biogas production, maximum biogas production rate, and concentration of amino acids and long-chain fatty acids in the waste-activated sludge. Four different doses were used: 0.043 gO₃ g_TSS^?1, 0.063 gO₃ g_TSS^?1, 0.080 gO₃ g_TSS^?1, and 0.100 gO₃ g_TSS^?1. The lower doses resulted in biogas production increases and a higher maximum biogas production rate in the anaerobic digestion of waste-activated sludge, while the contrary occurred at higher doses. The amino acids and long-chain fatty acids concentrations decreased when the ozone dose increased. The correlation with the ozone dose was nonlinear for amino acids and linear for long-chain fatty acids. The reaction products of long-chain fatty acids (aldehydes) are proposed as the cause of inhibition observed in the anaerobic digestion of waste-activated sludge treated with higher ozone doses.     

Start-up and Operation of Laboratory-Scale Thermophilic Upflow Anaerobic Sludge Blanket Reactors Treating Vegetable Processing Wastewaters

Thermophilic anaerobic treatment of hot vegetable processing wastewaters was studied in laboratory-scale UASB reactors at 55°C. The high-strength wastewater streams, deriving from steam peeling and blanching of carrot, potato and swede were used. The reactors were inoculated with mesophilic granular sludge. Stable thermophilic methanogenesis with about 60% COD removal was reached within 28 days. During the 134 day study period the loading rate was increased up to 24 kg COD m⁻³ day⁻¹. High treatment efficiency of more than 90% COD removal and concomitant methane production of 7·3 m³ CH₄ m⁻³ day⁻¹ were achieved. The anaerobic process performance was not affected by the changes in the wastewater due to the different processed vegetables. The results demonstrated the feasibility of thermophilic anaerobic treatment of vegetable processing wastewaters in UASB reactors. © 1997 SCI.     

煤制天然气废水的水解酸化法处理工艺

采用厌氧间歇式反应器,以煤制天然气（SNG）废水为处理对象,研究了在中温条件下水解酸化处理SNG废水后有机污染物的降解情况。以某柠檬酸生产厂废水厌氧反应器中的颗粒污泥为接种污泥进行4个月的驯化,形成处理SNG废水的稳定体系。试验结果表明运行温度为（35±1）℃,水解酸化时间为48h,进水CODcr总酚和挥发酚分别为1100、220和110mg／L的条件下,COD、总酚和挥发酚的去除率分别为45％、50％和99％左右,三者的降解均符合一级动力学特征。该体系主要停留在水解酸化阶段,甲烷产率为0．0025kgCHe／kgCODremoval,去除的TOC中有77％左右的有机碳用于污泥增殖,污泥增长率为0．3kgSS／kgCODremoval。     

Simultaneous removal of carbon,nitrogen and phosphorus from wastewater by coupling two-step anaerobic digestion with a sequencing batch reactor

The objective of this study was to develop an integrated process for simultaneous removal of carbon, nitrogen and phosphorus from industrial wastewaters. The process consisted of a-two step anaerobic digestion reactor, for carbon removal, coupled with a sequencing batch reactor (SBR) for nutrient removal. In the proposed process, carbon is eliminated into biogas by anaerobic digestion: acidogenesis and methanogenesis. The volatile fatty acids (VFA) produced during the first step of anaerobic digestion can be used as electron donors for both dephosphatation and denitrification. In the third reactor (SBR) dephosphatation and nitrification are induced through the application of an anaerobic–aerobic cycle. This paper describes the first trials and experiments on the SBR and a period of 210 days during which the SBR was connected to the acidogenic and methanogenic reactors. It was shown that nitrification of ammonia took place in the SBR reactor, during the aerobic phase. Furthermore, denitrification and VFA production were achieved together in the acidogenic reactor, when the efflux of nitrates from the SBR reactor was added to the first reactor influx. The proposed process was fed with a synthetic industrial wastewater, the composition of which was: total organic carbon (TOC)=2200 mg dm⁻³, total Kjeldahl nitrogen (TKN)=86 mg dm⁻³, phosphorus under phosphate form (P-PO₄)=20 mg dm⁻³. In these conditions, removals of carbon, nitrogen and phosphorus were 98%, 78% and 95% respectively. The results show that the combination of the two-step anaerobic digestion reactor and an SBR reactor is effective for simultaneous carbon, nitrogen and phosphorus removal. Reactor arrangements enabled zones of bacterial populations to exist. Complete denitrification occurred in the acidogenic reactor and hence the anaerobic activity was not reduced or inhibited by the presence of nitrate, thus allowing high TOC removal. Stable phosphorus release and phosphorus uptake took place in the SBR after coupling of the three reactors. A fast-settling compact sludge was generated in the SBR with the operational conditions applied, thus giving good separation of supernatant fluid. The benefits from this process are the saving of (i) an external carbon source for denitrification and phosphorus removal, (ii) a reactor for the denitrification step. © 1998 Society of Chemical Industry