The effect of pretreatment on anaerobic activity of olive mill wastewater using batch and continuous systems

This study was focused on several physico-chemical and biological treatment methods that may affect the reduction of the organic load in olive mill wastewater (OMW). In this study, removal of 95% of the phenolic compounds present in OMW was achieved using sand filtration and subsequent treatment with powdered activated carbon in a batch system. This pretreatment for OMW was found to enhance the anaerobic activity of the sludge in the batch system significantly. The efficiency of organic load removal achieved by the anaerobic treatment of untreated OMW in batch reactors with tap water dilution factors below 1:10, reached approximately 65% chemical oxygen demand (COD) removal. However, in the up-flow sludge anaerobic blanket (UASB) reactor, COD removal efficiency of 80–85% was reached at a hydraulic retention time (HRT) of 5 days with an influent COD concentration of 40 g l⁻¹ and organic loading rate (OLR)=8 g⁻¹ COD l⁻¹ per day.     

Detoxification of olive mill wastewaters by Moroccan yeast isolates

A total of 105 yeast strains were isolated from Moroccan olive oil production plants and evaluated for their ability to grow in olive oil mill wastewaters (OMW). The 9 isolates that grew best on OMW were selected for further study to evaluate their effect on removal of organic pollutants and OMW phytotoxicity (barley seed germination test). The results showed that at least four yeast isolates effectively lowered the toxicity of this effluent in addition to providing very useful materials in terms of both yeast biomass (6 g/l DW) and an irrigation fluid. This group of yeast isolates significantly reduced the concentration of total phenols (44% removal) and Chemical Oxygen Demand, COD (63% removal). The best germination rate of 80% for undiluted OMW was obtained for strain Candida holstii that also increased the pH from 4.76 to 6.75. Principal component analysis of the results obtained for the best yeast strains confirmed the importance of COD and total phenol reduction along with increase of organic nitrogen and final pH for the improvement of germination rates and phytotoxic reduction. This study has highlighted the potential of indigenous yeasts in detoxification of olive mill wastewaters.     

Phenolic removal in olive oil mill wastewater using loofah-immobilized Phanerochaete chrysosporium

Summary Olive oil mill wastewater (OMW) has a high organic load, and this is a serious concern of the olive industry. Conventional biological wastewater treatments, despite their simplicity and suitable performance are ineffective for OMW treatment since phenolics possess antimicrobial activity. In order to carry out a proper treatment of OMW, use of a microorganism able to degrade the phenolics is thus necessary. In this study the ability of Phanerochaete chrysosporium to degrade the phenolic compounds of OMW and to decrease the chemical oxygen demand (COD) using cells immobilized on loofah was examined. The basal mineral salt solution along with glucose, ammonium sulfate and yeast extract was used to dilute the OMW appropriately. The fungus did not grow on the concentrated OMW. The extent of removal in this bio-treatment, of total phenols (TP) and the COD were 90 and 50%, respectively, while the color and aromaticity decreased by 60 and 95%, respectively. The kinetic behavior of the loofah-immobilized fungus was found to follow the Monod equation. The maximum growth rate μ_max was 0.045 h⁻¹ while the Monod constant based on the consumed TP and COD were (mg/l) 370 and 6900, respectively.     

Effect of bioaugmentation of activated sludge with white-rot fungi on olive mill wastewater detoxification

AIMS: To test the potential use of Phanerochaete chrysosporium and other white-rot fungi to detoxify olive mill wastewaters (OMW) in the presence of a complex activated sludge. To combine the aerobic with anaerobic treatment to optimize the conversion of OMW in biogas. METHODS AND RESULTS: A 25-l air lift reactor was used to pretreat OMW by white-rot fungi. Detoxification of the OMW was monitored by size exclusion HPLC analysis, chemical oxygen demand (COD)/biological oxygen demand (BOD(5)) ratio evolution, and bioluminescence toxicity test. Anaerobic treatment of OMW was performed in a 12-l anaerobic filter reactor. Efficiency of the treatment was evaluated by organic matter removal, and biogas production. By comparison with the pretreatment by activated sludge only, the bioaugmentation with Phanerochaete chrysosporium or Trametes versicolor led to high removal of organic matter, decreased the COD/BOD(5) ratio and the toxicity. The subsequent anaerobic digestion of the OMW pretreated with activated sludge-white-rot fungi showed higher biomethanization yields than that pretreated with activated sludge only. Higher loading rates (7 g COD l(-1) day(-1)) were reached without any acidification or inhibition of biomethanization. CONCLUSIONS: The use of white-rot fungi, even in the presence of complex biological consortia to detoxify OMW, proved to be possible and made the anaerobic digestion of OMW for methane production feasible. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of fungi for OMW reuse and energy production could be adapted to industrial applications.     

Decolourization of Black Oxidized Olive-Mill Wastewater by a New Tannase-Producing Aspergillus flavus Strain Isolated from Soil

Summary By contaminating a Tunisian soil with black oxidized and sterilized olive-mill wastewaters (OMW), 30 new indigenous fungal soil strains able to overcome the OMW toxicity could be directly selected. Ten of the fungal strains previously isolated were screened for their capability to grow in a liquid culture medium containing oxidized OMW as the only source of carbon and energy. According to these preliminary tests, strain F2 showed the best capability of removing black colour and COD (chemical oxygen demand) and was further identified as Aspergillus flavus. After optimization of batch-liquid culture conditions in the presence of oxidized OMW, the time course of biomass and enzyme production by A. flavus F2 was followed in relation to colour and COD removal. A. flavus F2 could efficiently decolourize and detoxify the black oxidized OMW (58 and 46% of colour and COD removal, respectively, after 6 days of cultivation), concomitantly with the production of tannase (8000 UI/l on day 3).     

The use of hydroxyl-radical-generating systems for the treatment of olive mill wastewaters

Three hydroxyl-radical producing biomimetic systems, composed of CuII, hydrogen peroxide and pyridine, glucaric or succinic acid, were able to perform decolorization of olive mill wastewaters (OMW) >85 % within 3 d combined with a significant removal of total phenols (>75 %). The systems consisting of 50 mmol/L succinic acid, 5-10 mmol/L CuSO4 and 100 mmol/L H2O2 were the most effective at OMW treatment, and led to the reduction of phenol contents to <1 % along with high decolorization (>88 %) and acceptable values of chemical oxygen demand.     

Reduction of organic pollutants in Olive Mill Wastewater by using different mineral substrates as adsorbents

Physico-chemical treatments of Olive Mill Wastewater (OMW) were carried out using different inorganic substrates such as soil, bentonite and zeolite, in order to assess their efficiency to remove the organic load from OMW, in particular polyphenols (Pp) and to reduce chemical oxygen demand (COD). The effect of repeated treatments of OMW with different minerals and the possibility of regenerating them by the Low Temperature Ashing (LTA) technique, an eco-friendly procedure, for the reutilization of treated OMW, has been investigated. Zeolite was found to be highly efficient in adsorbing Pp and COD from OMW and was easy to regenerate by means of the LTA technique.     

Integrated biological process for olive mill wastewater treatment

The biological process for OMW treatment is based on an aerobic detoxification step followed by methanization step and aerobic post-treatment.The first aerobic detoxification step of OMW supplemented with sulfate and ammonium was carried out by the growth of Aspergillus niger in a bubble column. This step decreased OMW toxicity and increased its biodegradability because of phenolic compounds degradation. Growth of A. niger resulted in 58% COD removal, with production of biomass containing 30% proteins (w/w). Filtration of OMW was enhanced by this fermentation because the suspended solids were trapped in the mycelium. The filtrate liquid was then methanized using an anaerobic filter packed with flocoor. This reactor showed a short start up and a good stability. COD removal was around 60% and the methane yield (1 CH₄/g COD removed) was close to the theoretical yield.The anaerobic filter effluent was treated in an activated sludge fluidized reactor containing olive husk as a packing material. Husks were maintained in fluidization state by the aeration. This step induces COD removal at 45% and sludge (up to 2 g/dm³).The entire process allowed a global COD reduction up to 90%; however, the black colour due to polyphenolic compounds with high molecular weight persisted.     

Campylobacter and Arcobacter species in food-producing animals: prevalence at primary production and during slaughter

The presence of very high concentrations of organic pollutants, phenols, tannins and heavy metals mainly chromium in wastewater discharged from leather industries, tags it as one of the most polluting industries. The phenolic syntans discharged from tanning units have an adverse effect on living organisms and cause serious environmental pollution, thereby making it very imperative to remove it. Among various treatment methods available for removal of phenols, biodegradation is environment friendly. The present study aims at the remediation of phenolic syntan used in the leather industry employing individual as well as co-culture of Bacillus cereus and Pseudomonas aeruginosa at varying syntan concentration in the medium. Parameters such as chemical oxygen demand (COD), total organic carbon (TOC), total phenol content (TPC) and Fourier Transform Infrared Spectroscopy (FTIR) indicating biodegradation were analyzed. Promising results were observed with P. aeruginosa, which exhibited a reduction in TPC by 62–72% in all the concentrations of syntan tested just within 12 h of inoculation, whereas about 67 and 83% reduction in COD and TOC respectively was observed for 2000 ppm concentration at the end of 5 days. B. cereus also demonstrated very good reduction in the above parameters however; percentage was less as compared to P. aeruginosa. In the case of co-culture, the TPC reduction was higher than B. cereus but lesser than P. aeruginosa. The percentage reduction in TOC and COD was highest for 500 ppm which eventually decreased for subsequent concentrations.

     

Two-stage biological treatment of olive mill wastewater with whey as co-substrate

Olive mill wastewater (OMW) is a highly polluting wastewater, caused by a high organic load and phenol content. These characteristics suggest that it may be suitable for aerobic treatment and anaerobic bacterial digestion. Aerobic treatment coupled with anaerobic bacterial digestion may be economically feasible as the methane produced is a valuable energy source while simultaneously purifying the OMW. In an attempt to improve the overall performance of the process, the addition of a co-substrate such as whey to the aerobic treatment pre-treatment of OMW by the yeast Candida tropicalis was studied.The two-stage system operated satisfactorily up to an organic loading rate (OLR) of 3.0 kg COD L⁻¹ day⁻¹ with a biogas production rate of 1.25 L_biogas L_reactor⁻¹ day⁻¹ and a total COD reduction in excess of 93% (62% COD reduction in aerobic pretreatment and 83% COD reduction in anaerobic digestion). Fifty-four percent of the phenol was biodegraded during the aerobic treatment stage, and biogas with between 68% and 75% methane was produced during anaerobic digestion.     

Optimization of a biological process for treating potato chips industry wastewater using a mixed culture of Aspergillus foetidus and Aspergillus niger

Potato chips industry wastewater was collected and analyzed for biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) and total carbohydrates. Two Aspergillus species, A. foetidus and A. niger, were evaluated for their ability to grow and produce biomass and reduce the organic load of the wastewater. A. foetidus MTCC 508 and A. niger ITCC 2012 were able to reduce COD by about 60% and produce biomass 2.4 and 2.85 gl(-1), respectively. Co-inoculation of both Aspergillus strains resulted in increased fungal biomass production and higher COD reduction than in individual culture at different culture pH. pH 6 was optimum for biomass production and COD reduction. Amendment of the wastewater with different N and P sources, increased the biomass production and COD reduction substantially. Under standardized conditions of pH 6 and amendment of wastewater with 0.1% KH2PO4 and 0.1% (NH4)2 SO4, a mixed culture gave 90% reduction in COD within 60 h of incubation.     

Olive mill wastewater stabilization in open-air ponds: impact on clay-sandy soil

The aim of this work was to study the natural biodegradation of the stored olive mill wastewater (OMW) in ponds and the infiltration as well as the impact on soil of the effluent in the evaporation pond used for the storage over the past eight years. For this, two approaches were considered. First, a laboratory-scale column was used for the infiltration of OMW through soil (clay and sand) to predict the effect of the clayey soil in reducing OMW pollution. Second, the ponds including the effluent annually stored and having this clayey structure were investigated. At the laboratory-scale, a modification of OMW contents was noticed, with the elimination of 95% of total suspended solids (TSS), 60% of chemical oxygen demand (COD), 40% of total organic carbon (TOC), 50% of total P, 50% of phenols and 40% of minerals (K+, Mg++ and Na+). The experimented soil was able to restrain the considerable effects of OMW pollution. In the ponds, the granulometric characteristics, the physico-chemical and the biological parameters of the soil profile from the contaminated pond were compared to those of a control soil, located near the contaminated pond. Property modifications of the contaminated soil were noted, especially pH, electrical conductivity, COD and microflora. These changes can be explained by the infiltration of OMW constituents, which were noticed in the soil layers, especially phenolic compounds that have a negative effect on the ground water.     

Optimization of the fermentation of olive mill waste-waters by Aspergillus niger

Summary The fermentation of olive mill waste-waters (OMW) by Aspergillus niger was studied. On the basis of factorial design experiments, suspended solids and concentration of OMW, nitrogen source, sulphate and size of inocula were all found to be significant by affecting mycelium growth and chemical oxygen demand (COD) removal. Neither the absence of yeast extract, magnesium, sodium, potassium nor of calcium limited the growth of A. niger. With media lacking additional nitrogen and sulphate, the growth was limited. The optimal inoculum obtained was between 10⁶ and 10⁷ spores/g COD. The highest biomass and the greatest COD removal were obtained with removed COD to N:SO _inf4 ^sup¨- ratios averaging 100 to 3:1.5. Offprint requests to: M. Hamdi     

Biodegradation and detoxification of phenolic compounds by pure and mixed indigenous cultures in aerobic reactors

Degradation and detoxification of a mixture of persistent compounds (2-chlorophenol, phenol and m-cresol) were studied by using pure and mixed indigenous cultures in aerobic reactors. Biodegradation assays were performed in batch and continuous flow reactors. Biodegradation was evaluated by determining total phenols, ultraviolet spectrophotometry and chemical oxygen demand (COD). Microbial growth was measured by the plate count method. Scanning electronic microscopy was employed to observe the microbial community in the reactor. Detoxification was evaluated by using Daphnia magna toxicity tests. Individual compounds were degraded by pure bacteria cultures within 27 h. The mixture of 2-clorophenol (100 mgl⁻¹), phenol (50 mgl⁻¹) and m-cresol (50 mgl⁻¹) was degraded by mixed bacteria cultures under batch conditions within 36 h: 99.8% of total phenols and 92.5% of COD were removed; under continuous flow conditions 99.8% of total phenols and 94.9% of COD were removed. Mineralization of phenolic compounds was assessed by gas chromatography performed at the end of the batch assays and in the effluent of the continuous-flow reactor. Toxicity was not detected in the effluent of the continuous-flow reactor.     

Use of native aquatic macrophytes in the reduction of organic matter from dairy effluents

Considering the diversity and the unexplored potential of regional aquatic flora, this study aimed to identify and analyze the potential of native aquatic macrophytes to reduce the organic matter of dairy wastewater (DW) using experimental constructed wetlands. The dairy wastewater (DW) had an average chemical oxygen demand (COD) of 7414.63 mg/L and then was diluted to 3133.16 mg/L (D1) and to 2506.53 mg/L (D2). Total solids, COD, temperature, and pH analyses were performed, and the biochemical oxygen demand (BOD) was estimated from the COD values. The best performance in the reduction of the organic matter was observed for Polygonum sp. (87.5% COD and 79.6% BOD) and Eichhornia paniculata (90% COD and 83.7% BOD) at dilution D1, on the 8th day of the experiment. However, the highest total solids removal was observed for Polygonum sp. (32.2%), on the 4th day, at dilution D2. The total solid (TS) concentration has also increased starting from the 8th day of the experiment was observed which may have been due to the development of mosquito larvae and their mechanical removal by sieving, thus changing the steady state of the experimental systems. The macrophytes Polygonum sp. and E. paniculata were considered suitable for the reduction of organic matter of DW using constructed wetlands.     

Enhanced remediation of black liquor by activated sludge bioaugmented with a novel exogenous microorganism culture

Black liquor (BL) is a notoriously difficult wastewater to treat due to the economic and efficiency limitations of physiochemical methods and intrinsic difficulties with bioremediation strategies caused by the high pH (10–13) and lignin content. This study investigated the feasibility of a novel bioaugmentation strategy for BL treatment, which uses a mixed microorganism culture of lignocellulose-degrading microorganisms isolated from degraded bamboo slips. Black liquor treatment was assessed in terms of chemical oxygen demand (COD) and color removal with a sequencing batch reactor organic loading rate of 9 kg COD/L·day under highly alkaline conditions (pH?10). Results revealed that bioaugmented activated sludge treatment of BL with special mixed microorganisms significantly enhanced the removal efficiency of COD, color, and lignin from the wastewater up to 64.8, 50.5, and 53.2 %, respectively. Gel permeation chromatography profiles showed that the bioaugmentation system could successfully degrade high molecular lignin fragments in black liquor. This work confirms bioaugmentation as a feasible alternative strategy for enhanced biological treatment of wastewater with high lignin content and high organic load rate under strongly alkaline conditions.     

Operational factors and nutrient effects on activated sludge treatment of Pinus radiata kraft mill wastewater

The biodegradability of Pinus radiata bleached kraft mill wastewater by an activated sludge treatment during a period of 280 days was evaluated. The effect of varying hydraulic retention time (HRT) in the range of 48 to 4.5 h and nitrogen (N) and phosphorus (P) addition on removal of biological oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (TSS and VSS), total phenolic compounds, tannin and lignin and reduction of toxicity was investigated. Removal of BOD5 was higher than 90% when HRT varied from 16 to 6 h, but decreased when HRT was less than 6 h. Similar performance was observed for COD removal, which was about 60% when HRT was varied from 16 to 6 h. Removal of total phenolic compounds and tannin and lignin was seriously affected by HRT. N and P addition to maintaining a ratio of 100:5:0.3 provided optimal BOD5, COD and suspended solids removal when HRT varied from 16 to 7 h, and no toxicity (using Daphnia) was detected in the treated effluent. When HRT was less than 6 h, the system showed destabilisation and pH, COD, BOD5 and suspended solids removal decreased.     

Effect of clay pretreatment on photofermentative hydrogen production from olive mill wastewater

The aim of this paper was to gain further insight into the effect of the clay pretreatment process on photofermentative hydrogen production. This two-stage process involved a clay pretreatment step followed by photofermentation which was performed under anaerobic conditions with the illumination by Tungsten lamps. Rhodobacter sphaeroides O.U.001 was used for photofermentation. Higher amounts of color (65%), total phenol (81%) and chemical oxygen demand (31%) removal efficiencies were achieved after clay pretreatment process. During photofermentative hydrogen production with the effluent of clay pretreatment process, the main organic compounds resulting higher hydrogen production rates were found to be acetic, lactic, propionic, and butyric acids. Compared to photofermentation using raw olive mill wastewater ( 16LH2/LOMW), the amount of photofermentative hydrogen production was doubled by using the effluent of the clay pretreatment process (31.5LH2/LOMW). The reasons for the improvement of hydrogen production by clay treatment can be attributed to the high removal of the hardly biodegradable compounds such as phenols; minor removal of organic acids, sugars and amino acids that are known to enhance photofermentative hydrogen production; and the color depletion of raw OMW which might cause a shadowing effect on the photosynthetic bacteria.     

Anaerobic digestion challenge of raw olive mill wastewater

Olive mill wastewater (OMW) was digested in its original composition (100% v/v) in an anaerobic hybrid. High concentrations (54–55 kg COD m⁻³), acid pH (5.0) and lack of alkalinity and nitrogen are some OMW adverse characteristics. Loads of 8 kg COD m⁻³ d⁻¹ provided 3.7–3.8 m³ biogas m⁻³ d⁻¹ (63–64% CH₄) and 81–82% COD removal. An effluent with basic pH (8.1) and high alkalinity was obtained. A good performance was also observed with weekly load shocks (2.7–4.1, 8.4–10.4 kg COD m⁻³ d⁻¹) by introducing piggery effluent and OMW alternately. Biogas of 3.0–3.4 m³ m⁻³ d⁻¹ (63–69% CH₄) was reached.Developed biomass (350 days) was neither affected by raw OMW nor by organic shocks. Through the effluents complementarity concept, a stable process able of degrading the original OMW alone was obtained. Unlike what is referred, OMW is an energy resource through anaerobiosis without additional expenses to correct it or decrease its concentration/toxicity.     

Behavior of aromatic compounds contained in kraft mill effluents treated by an aerated lagoon

Kraft mill effluents were biologically treated in an aerated lagoon (AL) (3.4 L) to evaluate the behavior of aromatic compounds by UV-vis spectroscopy. Under aerobic conditions, biological oxygen demand (BOD(5)) removal was between 84% and 95%, whereas soluble chemical oxygen demand (COD(s)) removal ranged between 40% and 60%. A slight increase was observed in the VIS(436)/COD(s) relationship (0.101-0.110), indicating that color reduction was less than the total organic matter reduction expressed by COD(s). Additionally, low values of UV(254)/UV(280) (1.23-1.12) indicate the presence of lignin-derived compounds in the aerobic effluent relationship. Ultrafiltration (UF) analysis shows that color was concentrated in the molecular weight fraction larger than 10,000 Da. The recalcitrant fraction was found to be resistant to further biodegradation, even under optimized microbiological conditions.