Elimination of polyphenols toxicity from olive mill wastewater sludge by its co-composting with sesame bark

Olive mill wastes represent a significant environmental problem in Mediterranean areas where they are generated in huge quantities in a short period of time. Their high phenol, lipid and organic acid concentrations turn them into phytotoxic materials, but these wastes also contain valuable resources such as a large proportion of organic matter and a wide range of nutrients that could be recycled. Composting is one of the technologies used for the valorization of this effluent, producing a fertilizer useful for poor soils.The present work deals with the changes that occur in the content of phenolic compounds and the biotoxicity of the oxidized substrate which result from the composting of olive mill wastewater (OMW) sludge with sesame bark. The total organic matter decreased 52.72% while water-soluble phenol degradation decreased 72% after 7 months of processing. Gas chromatography coupled with mass spectroscopy was used to confirm the elimination of polyphenols during composting. Initially, the analysis showed three abundant polyphenolic compounds, one of which was identified as the 4-hydroxyphenyl-ethanol (tyrosol), a well-known antioxidant in OMW. After 7 months of composting, all of the phenolic compounds disappeared. The phytotoxic effects of OMW sludge, assessed by the plant index germination, increased during the composting to reach 80% after 210 days. This trend was confirmed by the correlation between physico-chemical and toxicity parameters. The results obtained confirmed the stability of the compost prepared from OMW sludge with sesame bark and indicated a gradual detoxification as the compost matured.     

Analysis of heavy metals during composting of the tannery sludge using physicochemical and spectroscopic techniques

The major limitation of direct application of tannery sludge compost in agriculture is the total heavy metal contents and their bioavailability to the soil-plant system. This study focused on the heavy metal characterization and the influence of changing the physicochemical properties of the medium throughout the composting on the concentrations, bioavailability or chemical forms of Cr, Cu, Zn, Pb and Cd in tannery sludge. The study shows that throughout the 60 days of composting, physicochemical analysis and Fourier-transformed infrared (FTIR) spectroscopic characterization show that all parameters elaborated and reached relatively stable levels reflecting the stability and maturity of the final product, and revealed the biodegradation of components that can be easily assimilated by microorganism. The C/N ratio reaches the optimal range of stable compost; inorganic nitrogen is transformed into stable organic forms. The total concentration of Cr, Zn, Cu, Pb and Cd is very low rendering final compost acceptable for agricultural use. The germination index for both Chinese cabbage and lettuce was 97% after 60 days of composting, showing that the final compost was not phytotoxic. Furthermore, in using a sequential extraction method in sludge compost at different phases of treatment, a less than 2% of metals bound to bioavailable fractions X-(KNO(3)+H(2)O). A large proportion of the heavy metals were associated to the residual fraction (75-85%) and more resistant fractions to extraction X-NaOH, X-EDTA, X-HNO(3) (15-25%). Mobile fractions of metals are poorly predictable from the total content. Bioavailability of all fractions of elements tends to decrease.     

Phytotoxicity and speciation of copper, zinc and lead during the aerobic composting of sewage sludge

The content and speciation of heavy metals in composted sewage sludge is the main cause of negative impacts on environment and health of animal and human. An aerobic composting procedure was conducted to investigate the influences of some key parameters on phytotoxicity and speciation of Cu, Zn and Pb during sewage sludge composting. The pH value reached the optimal range for development of microorganisms, and content of organic matter (OM) and dissolved organic carbon (DOC) decreased with the composting age. The total amounts of Cu, Zn and Pb were much lower in the final compost. The results from sequential extraction procedure of heavy metals showed that composting process changed the distribution of five fractions of Cu, Zn and Pb, and reduced the total contents and sum percentages of four mobile fractions (exchangeable (EXCH), carbonate (CAR), reducible iron and manganese (FeMnOX), and organic matter bound (OMB)), indicating that the metal mobility and phytotoxicity decreased after aerobic composting. The seed germination and root growth of Pakchoi (Brassica Chinensis L.) were enhanced with composting age and reached the highest value at the end of compost. The decrease of OM and DOC was significantly correlated to changes of metal distribution and germination index (GI) of Pakchoi. Only for Cu in the compost, the GI could be predictable from the sum mobile metal fractions (EXCH+CAR+FeMnOX+OMB) (R=-0.814(*)). For Zn and Pb, R value was significantly increased by use of other components, such as pH, OM and DOC, which suggested that the transformation of heavy metal speciation and phytotoxicity of sewage sludge during an aerobic composting was rather strongly dependent on multiple components than a single element.     

Eliminating toxic compounds by composting olive mill wastewater-straw mixtures

The present work studies the changes occurring in organic matter, phenols and biotoxicity on composting olive mill wastewater with barley straw. The total organic matter decreased, a drop of 25% was reached after the stabilization phase and 52% at the end of the maturation phase. Degradation of the phenols reached 54% and 95%, respectively, after these periods. The toxicity of the water extract, evaluated by the Photobacterium phosphoreum fluorescence, decreased to disappear after only 2 months of composting. This trend was confirmed by the tight correlation between the physico-chemical and toxicity parameters, indicating that the degradation of organic matter leads to a strong reduction of the C/N ratio and of toxicity. The results obtained indicate a normal process of humification occurring during the composting of the formerly highly toxic olive mill wastewater-straw mixture and resulting in a product, which has good agricultural properties as organic fertilizer.     

Evaluation of pilot-scale in-vessel composting for food waste treatment

This study is aimed to evaluate the performance of pilot-scale in-vessel composting for food wastes treatment. The composting plant was installed with 324 m3 of the composting bay volume and 14,000 kg/day of the composting material flow rate. The evaluations studied included the operational indices, the compost maturity indices, and the quality of the final compost. Blowers of this system were useful in maintaining aerobic condition (over 6% oxygen concentration in off-gas) through the entire compost bay. The levels of indices evaluated remained constant in the final part of composting. The final compost was satisfactory for its agricultural application. It was revealed in this study that bulk density bore a linear relation to moisture content during composting, and the final compost without bulking agent showed negative correlation between heavy metal and organic matters content.     

Elemental and spectroscopic characterization of humic-acid-like compounds during composting of olive mill by-products

Humic acids (HAs) were isolated at different stages of composting from two piles of solid olive mill residues (SOR) treated for the first 30 days with tap water (pile C1) or olive mill wastewater (pile C2), for a total composting period of 9 months. The HA fractions were characterized by elemental analysis, UV-visible, Fourier transform infrared and fluorescence spectroscopy in order to monitor humification process and the maturity of the composts. As composting proceeded, the elemental composition of the humic acids showed a decrease in C and H content, and in the C/N ratio, and an increase in N and O contents and in the C/H and O/C ratios. These changes could be attributed to a loss of aliphatic groups and to an increase of aromatic character, polycondensation and degree of oxidation of the HAs. Spectroscopic data agree and support these results, suggesting that the chemical and structural features of the HAs of both composts tend to reach those typical of native soil HAs, that is compounds with a high degree of humification and a high molecular weight and complexity. Therefore, both composting processes seem suitable to produce well-humified organic matter, with important benefits for their use in soil amendment. No differences appeared between the two treatments concerning the humic character of the two final composts.     

Bioremediation of endosulfan contaminated soil and water -- optimization of operating conditions in laboratory scale reactors

A mixed bacterial culture consisted of Staphylococcus sp., Bacillus circulans-I and -II has been enriched from contaminated soil collected from the vicinity of an endosulfan processing industry. The degradation of endosulfan by mixed bacterial culture was studied in aerobic and facultative anaerobic conditions via batch experiments with an initial endosulfan concentration of 50mg/L. After 3 weeks of incubation, mixed bacterial culture was able to degrade 71.58+/-0.2% and 75.88+/-0.2% of endosulfan in aerobic and facultative anaerobic conditions, respectively. The addition of external carbon (dextrose) increased the endosulfan degradation in both the conditions. The optimal dextrose concentration and inoculum size was estimated as 1g/L and 75mg/L, respectively. The pH of the system has significant effect on endosulfan degradation. The degradation of alpha endosulfan was more compared to beta endosulfan in all the experiments. Endosulfan biodegradation in soil was evaluated by miniature and bench scale soil reactors. The soils used for the biodegradation experiments were identified as clayey soil (CL, lean clay with sand), red soil (GM, silty gravel with sand), sandy soil (SM, silty sand with gravel) and composted soil (PT, peat) as per ASTM (American society for testing and materials) standards. Endosulfan degradation efficiency in miniature soil reactors were in the order of sandy soil followed by red soil, composted soil and clayey soil in both aerobic and anaerobic conditions. In bench scale soil reactors, endosulfan degradation was observed more in the bottom layers. After 4 weeks, maximum endosulfan degradation efficiency of 95.48+/-0.17% was observed in red soil reactor where as in composted soil-I (moisture 38+/-1%) and composted soil-II (moisture 45+/-1%) it was 96.03+/-0.23% and 94.84+/-0.19%, respectively. The high moisture content in compost soil reactor-II increased the endosulfan concentration in the leachate. Known intermediate metabolites of endosulfan were absent in all the above degradation studies.     

Utilization of olive mill sludge in manufacture of lignocellulosic/polypropylene composite

This study evaluated some physical and mechanical properties of injection-moulded polypropylene (PP) composites reinforced with various mixtures of the wood flour (WF) and the olive mill sludge (OMS). Water resistance of the composites improved by the increasing OMS flour content. However, the flexural properties of the composites decreased with increasing OMS flour content. The addition of a coupling agent improved the compatibility between the lignocellulosic material and PP through esterification and thus reduced the water absorption and improved the stability and mechanical properties. The findings obtained in the study showed that the OMS was capable of serving as new reinforcing filler in the manufacturing of thermoplastic polymer composites.     

Compost produced from organic fraction of municipal solid waste, primary stabilized sewage sludge and natural zeolite

The aim of this work is to present the physicochemical characteristics of the compost produced from dewatered anaerobically stabilized primary sewage sludge (DASPSS), organic fraction of municipal solid waste (OFMSW) and the metal uptaken by zeolite (clinoptilolite). The final results indicated that the composted material produced from clinoptilolite 20% w/w and 80% w/w DASPSS and OFMSW (60% and 40%, respectively) provided better soil conditioning compared to the compost produced from DASPSS. The co-composting products had a higher concentration of total humic and organic matter (O.M.) than the sewage sludge compost. Also, the heavy metals concentration in the final products was in lower concentration than in the sewage sludge compost. The zeolite appeared to uptake a significant (p<0.05) amount of metals. Specifically, the use of 20-25% w/w of clinoptilolite appears to uptake 100% of Cd, 10-15% of Cr, 28-45% of Cu, 41-47% of Fe, Mn 9-24% of Mn, 50-55% of Ni and Pb, and 40-46% of Zn. Although by the application of the composting process, the reduction in dry mass is between 30% and 40% for all samples.     

Microbial inoculum with leachate recirculated cultivation for the enhancement of OFMSW composting

Traditional composting operation may take over 2 weeks for the primary stage. The enhancement of the composting process will shorten the operation time and thus reduce the composting space and production costs. In this work, a microbial inoculum originated from the MSW leachate was used for the enhancement of the biodegradation of organic fractions of MSW (namely OFMSW hereinafter) in the composting process. The leachate generated from OFMSW composting was cultivated in the presence of foreign nutritions of beef extract, peptone, K(2)HPO(4) and CaCO(3), respectively. The rough microbial inoculum was then harvested from the cultivated leachate and employed for the enhancement of OFMSW composting. One percent of the rough inoculum was mixed with 99% of the organic wastes (on wet basis). When the composting process proceeded at Day 7, the leachate thus generated was re-cultivated with the said nutrition and introduced into fresh organic wastes for another 7-day composting; repeating this step and the final generated leachate (namely final inoculum) was used for the fresh organic waste composting process. Seeding effects in terms of composting parameters (temperature, oxygen uptake rate, pH, cellulase, microbial numbers, moisture content, and nitrogen concentrations) were tested and the data were collected as reported in this paper. It was found that the temperature in the composting system seeded with the final inoculum could reach over 55 degrees C for the duration of over 96 h, and the numbers of thermophilic bacteria, actinomyces and molds in the refuse, increased by approximately 100%, 70% and 50%, respectively, after a 20-day primary composting. pH maintained at 7.0 with slight fluctuation, thus facilitating the microbial behaviors of cellulose depletion. Meanwhile, the oxygen uptake rate (OUR) and cellulase activity was observed to increase by some 50% and 26%, respectively. The development trend of nitrogen concentrations also indicated that the microorganisms in the final inoculum had the ability to endure the extreme temperature of 70 degrees C. Hence, it can be concluded that the final inoculum developed with leachate recirculated cultivation can work well, benefited from the indigenous communities present to efficiently accelerate the OFMSW composting process.     

Modeling of zinc solubility in stabilized/solidified electric arc furnace dust

The bacteria that could grow on media containing olive mill wastewater (OMW) were isolated and their lipase production capacities were investigated. The strain possessing the highest lipase activity among 17 strains grown on tributyrin agar medium was identified as Bacillus sp. The effect of initial pH on the lipase activity was investigated in tributyrin medium and pH 6 was found to be the optimal. The liquid medium composition was improved by replacing tributyrin with various carbon sources. Among the media containing different compositions of triolein, trimyristin, trilaurin, tricaprin, tricaprylin, tributyrin, triacetin, Tween 80, OMW, glucose, and whey; the medium contained 20% whey +1% triolein was found to give the highest lipase activity. Cultivation of Bacillus sp. in the optimal medium at pH 6 and 30 degrees C for 64h resulted in the extracellular and intracellular lipase activities of 15 and 168U/ml, respectively.     

Bioremediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated sewage sludge by different composting processes

The efficiency of four different composting processes to bioremediate polycyclic aromatic hydrocarbons (PAHs)-contaminated sewage sludge was investigated. Prior to composting, sewage sludge coming from the Datansha wastewater treatment plant, Guangzhou, China, was mixed with rice straw to obtain a C/N ratio of 13:1. After 56 days of composting, the total concentrations of 16 PAHs (Sigma(PAHs)) ranged from 1.8 to 10.2 mg kg(-1) dry weight, decreasing in order of inoculated-manual turned compost (IMTC)>manual turned compost (MTC)>continuous aerated compost (CAC)>intermittent aerated compost (IAC), exhibiting removal rates of 64%, 70%, 85% and 94%, respectively. Individual PAHs were generally removed in similar rates. IAC treatment showed a higher removal rate of high molecular weight PAHs and carcinogenic PAHs comparing to the other composting processes.     

Emission of volatile organic compounds from composting of different solid wastes: abatement by biofiltration

Emission of volatile organic compounds (VOCs) produced during composting of different organic wastes (source-selected organic fraction of municipal solid wastes (OFMSW), raw sludge (RS) and anaerobically digested wastewater sludge (ADS) and animal by-products (AP)) and its subsequent biofiltration have been studied. Composting was performed in a laboratory scale composting plant (30l) and the exhaust gases generated were treated by means of a compost biofilter. VOCs concentration in the composting exhaust gases for each composting process ranged from 50 to 695 mg C m-3 for OFMSW (5:1), from 13 to 190 mg C m-3 for OFMSW (1:1), from 200 to 965 mg C m-3 for RS, from 43 to 2900 mg C m-3 for ADS and from 50 to 465 mg C m-3 for AP. VOCs emissions were higher during the beginning of the composting process and were not generally related to the biological activity of the process. These emissions corresponded to an average loading rate applied to the biofilter from 2.56 to 29.7 g C m-3 biofilter h-1. VOCs concentration in the exhaust gas from the biofilter ranged from 55 to 295 mg C m-3 for OFMSW (5:1), from 12 to 145 mg C m-3 for OFMSW (1:1), from 55 to 270 mg C m-3 for RS, from 42 to 855 mg C m-3 for ADS and from 55 to 315 mg C m-3 for AP. Removal efficiencies up to 97% were achieved although they were highly dependent of the composted waste. An important observation was that the compost biofilter emitted VOCs with an estimated concentration of 50 mg C m-3.     

Impact of fresh and composted solid olive husk and their water-soluble fractions on soil heavy metal fractionation; microbial biomass and plant uptake

The use of waste materials as organic amendments in soil remediation can affect metal solubility; this interaction will vary with the characteristics of the organic matter that is added to the soil. A pot experiment was carried out in a calcareous, metal-polluted soil, using Beta maritima L. as an indicator species for the treatment effects on metal solubility. The treatments were: fresh solid olive husk, a mature compost, their respective water extracts (as the most reactive and biodegradable fraction) and an unamended, control soil. The compost reduced metal availability and plant uptake, while fresh olive husk favoured Mn bioavailability and produced phytotoxicity. The water-soluble extract from fresh solid olive husk also provoked elevated Mn solubility in soil, but did not increase Mn uptake by plants. The application of water-soluble organic matter obtained from compost did not affect heavy metal solubility significantly. Therefore, composted olive husk seems to be the most-appropriate material for the development of bioremediation strategies.     

An analysis of synergistic and antagonistic behavior during BTEX removal in batch system using response surface methodology

The removal of benzene, toluene, ethylbenzene and xylene (BTEX) as quaternary mixtures were studied in batch systems using a well-defined mixed microbial culture. The synergistic and antagonistic effects of total BTEX removal (BTEXT-RE) due to the presence of mixed substrate was evaluated through experiments designed by response surface methodology (RSM). The low and high concentrations of individual BTEX were 15 and 75 mg l(-1), respectively. The results showed that, increasing the concentration of xylene increased the cumulative BTEX removal (BTEXT-RE), however the reverse occurred when benzene concentrations were increased from low to high levels. A mixed response of increasing and decreasing trend in the BTEXT-RE value was observed when either of toluene or ethylbenzene concentration was increased. When the concentrations of individual BTEX compounds were 30 mg l(-1), the BTEXT-RE was about 58%. Complete BTEXT-RE was achieved at optimal BTEX concentrations of 48.1, 45.6, 49.3 and 56.6 mg l(-1). The RSM approach was found efficient in explaining the main, squared and interaction effects among individual BTEX concentrations on the BTEXT-RE in a more statistically meaningful way.     

Effect of compost age and composition on the atrazine removal from solution

Compost samples from two composting facilities, the Urbana (Illinois) Landscape Recycling Center (ULRC) and Illinois State University (ISU), were selected to examine the effect of compost age on atrazine removal from solution. The ULRC samples were made from yard waste without an additional nitrogen source. The ISU samples were made from yard waste or sawdust with the addition of manure. The 6-month-old ULRC compost had the greater capacity to remove atrazine from solution, which we attributed to its greater organic carbon content. The addition of nitrate into ULRC compost could influence the extent of atrazine removal, but did not have a significant impact on atrazine removal when applied to ISU compost, probably because manure was added to the yard waste to produce the compost. For both ULRC and ISU samples, the presence of sodium azide inhibited atrazine removal, suggesting that microbial activity contributed to the atrazine removal. Metabolic analysis demonstrated that hydroxyatrazine was the major identified metabolite that accumulated in solution before significant ring mineralization could occur. When compared with the ISU compost, the ULRC compost sample had a greater capacity to remove atrazine from solution during the 120 days of study because of the larger humic acid content. The experimental results suggested that less-mature compost may be better suited for environmental applications such as removing atrazine from tile-drainage waters.     

Concentration and speciation of heavy metals in six different sewage sludge-composts

This study presents the concentrations and speciation of heavy metals (HMs) in six different composts of sewage sludges deriving from two wastewater treatment plants in China. After 56 days of sludge composting with rice straw at a low C/N ratio (13:1), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) were enriched in sludge composts, exhibiting concentrations that varied from 0.75 to 2.0, 416 to 458, 66 to 168 and 1356 to 1750mgkg(-1) dry weight (d.w.), respectively. The concentrations increased by 12-60% for Cd, 8-17% for Cu, 15-43% for Pb and 14-44% for Zn compared to those in sewage sludges. The total concentrations of individual or total elements in the final composts exceeded the maximum permissible limits proposed for compost or fertilizer. In all the final composts, more than 70% of total Cu was associated with organic matter-bound fraction, while Zn was mainly concentrated in exchangeable and Fe-Mn oxide-bound fractions which implied the high mobility and bioavailability. Continuously aerated composting treatment exhibited better compost quality and lower potential toxicity of HMs, whereas inoculant with microorganism and enzyme spiked during composting had no obvious advantage on humification of organic matter and on reducing HM mobility and bioavailability.     

Microbial community dynamics during composting of sewage sludge and straw studied through phospholipid and neutral lipid analysis

The composting process involves a succession of different communities of microorganisms that decompose the initial material, transforming it into a stable final product. In this work, the levels of phospholipid fatty acid (PLFA), neutral lipid fatty acid (NLFA) and sterol were monitored in compost versus time, as indicators of the activity of various microorganisms (Gram-positive or Gram-negative bacteria, fungi, etc.). During composting, the PLFA and NLFA from Gram-negative bacteria and eukaryotes (2-OH 10; 3-OH 12; 2-OH 14; 13:0; 16:1; 18:1 trans) as well as some sterols of plant origin (e.g. monostearin sterols) decreased until the end of composting. In contrast, the branched fatty acids with iso- and anteiso-forms (i-15:0; a-15:0; i-16; i-17) increased mainly in the thermophilic phase, but decreased right after. The PLFA 18:2 (6; 9), which is used as an index of the occurrence of some fungi, rose strongly at the beginning of composting, but fell after peak heating. In contrast, the other main sterol indicative of fungi, ergosterol, decreased at the beginning of the thermophilic phase, but increased strongly by the end of composting. Accordingly, cluster and PCA analysis separated the PLFA of Gram-negative bacteria and eukaryotic cells from those of Gram-positive bacteria and long-chain fatty acids. The fungal PLFA considered, 18:2 (9, 12), was clustered more closely to iso- and anteiso-branched PLFAs. Stigmasterol, squalene and cholesterol occurred in the lower right part of the loading plot and were clustered more closely to iso-, anteiso-branched PLFAs and 18:2 w 6,9 suggesting their relationship to microbial activities. We also observed the tendency of resistance of fatty acid PLFAs and NLFAs of long chain (19:0 (cis-9); 20:0) and some recalcitrant sterols, e.g. sitosterol, at the end of composting. The presence of high levels of the latter in the final stage indicates their contribution to the structural stability of organic matter fractions. These recalcitrant components were more clustered and occurred in the lower right part of the loading plot.     

Synthesis of Olive‐Like Nitrogen–Doped Carbon with Embedded Ge Nanoparticles for Ultrahigh Stable Lithium Battery Anodes

The development of environment‐friendly and high‐performance carbon materials for energy applications has remained a great challenge. Here, a novel and facile method for synthesis of olive‐like nitrogen‐doped carbon embedded with germanium (Ge) nanoparticles using widespread and nontoxic dopamine as carbon and nitrogen precursors is demonstrated, especially by understanding the tendency of pure GeO₂ nanoparticles forming ellipsoidal aggregation, and the chelating reaction of the catechol structure in dopamine with metal ions. The as‐synthesized Ge/N‐C composites show an olive‐like porous carbon structure with a loading weight of as high as 68.5% Ge nanoparticles. A lithium ion battery using Ge/N‐C as the anode shows 1042 mAh g^?1 charge capacity after 2000 cycles (125 d) charge/discharge at C/2 (1C = 1600 mA g^?1) with a capacity maintaining efficiency of 99.6%, significantly exceeding those of the previously reported Ge/C‐based anode materials. This prominent cyclic charge/discharge performance of the Ge/N‐C anode is attributed to the well‐dispersed Ge nanoparticles in graphitic N‐doped carbon matrix, which facilitates high rates (0.5–15 C) of charge/discharge and increases the anode structure integrity. The synthesis strategy presented here may be a very promising approach to prepare a series of active nanoparticle–carbon hybrid materials with nitrogen doping for more and important applications.     

The use of composting for the treatment of animal by-products: Experiments at lab scale

Animal by-products (ABP), containing mainly rabbit and chicken carcasses were composted at laboratory scale. Results indicate that if proper conditions are used, wastes can be successfully composted and stabilised meeting current European hygienisation standards regarding the disposal of this type of wastes. During the process, temperatures above 60 degrees C were easily reached and maintained for 2 days at least, due to the high energy potential of these materials. However, care must be taken to ensure that these temperatures are reached in the entire reactor to guarantee proper hygienisation of the material. These high temperatures may bring about operational problems such as moisture losses due to very high airflows required for their control. Biological activity indices, such as respiration index (RI) and oxygen uptake rate (OUR) used for the monitoring of the process, were able to indicate potential and actual conditions within the composting reactor, respectively.