Effect of the addition of fatty by-products from the refining of vegetable oil on methane production in co-digestion.

The purpose of this work was to investigate the effects of the addition of by-products from the refining of vegetable oil on the behavior of co-digestion reactors treating a mixture of grass, cow dung and fruit and vegetable waste. Three by-products were used: one soapstock, one used winterization earth and one skimming of aeroflotation of the effluents. Three 15 l reactors were run in parallel and fed five times a week. In a first phase of 4 weeks, the three reactors were fed with the co-digestion substrates alone (grass, cow dung and fruit and vegetable waste) at an organic loading rate (OLR) of 1.5 g VS/kg d (VS: volatile solids). Then, a different by-product from the refining of oil was added to the feed of each reactor at an OLR of 0.5 g VS/kg d, generating a 33% increase in the OLR. The results show that the addition of by-products from the refining of oil is an efficient way of increasing the methane production of co-digestion reactors thanks to high methane yield of such by-products (0.69-0.77 l CH(4)/g VS loaded). In fact, in this work, it was possible to raise the methane production of the reactors by about 60% through a 33% increase in the OLR thanks to the addition of the by-products from the refining of vegetable oil.

Treatment of fatty solid waste from the meat industry in an anaerobic sequencing batch reactor: start-up period and establishment of the design criteria.

An anaerobic sequencing batch reactor (AnSBR) was used to treat the dissolved air flotation skimmings from a cooked pork meat plant. During the start-up period, the reactor was operated in fed-batch mode for 25 days and 7 batches were treated. The SBR was inoculated with sludge taken from a reactor treating distillery vinasse. The results showed that this kind of sludge is a very good source of inoculum for digesters treating residues with a high content in fats and long-chain fatty acids because it was able to adapt very rapidly to the new substrate and, from the second batch on, the sludge was already able to metabolize the fatty residue at quite high rates. The AnSBR was then operated with 5 batches per week for 110 days and the quantity of VS added per batch was regularly increased until the maximum treatment capacity of the reactor (i.e. maximum loading rate) was reached. The maximum organic loading rates were found to be 0.16 g VS/g VSS d, or 0.224 g VS/g VSS.batch when the reactor is fed 5 times a week. The biodegradability of the skimmings was very high, with more than 97% of TS removal, and the methane production was 880+/-90 mL of methane/g of VS(added).

Potentially toxic elements in commonly consumed fish species from the western Mediterranean Sea (Almería Bay): Bioaccumulation in liver and muscle tissues in relation to biometric parameters.

Marine pollution is one of today's most relevant problems. Public awareness has been raised about the harmful potential of heavy metals (HMs) accumulating in edible fish and possibly ending up in human diet through the food chain. This study aimed to characterize and evaluate As, Cd, Cr, Cu, Ni and Pb contents in four edible fish species from the western Mediterranean Sea. Liver and muscle toxic elements were determined by GF-AAS in Mullus surmuletus, Merluccius merluccius, Auxis rochei and Scomber japonicus from Almería Bay (Spain). Muscular composition, biometrics and trophic levels were also determined. The mean PTE concentration levels (mg kg-1, DW) in fish muscle tissue were: As (2.90-53.74), Cd (0.01-0.18), Cr (0.53-2.01), Cu (0.78-6.93), Ni (0.06-0.24), Pb (0.0-0.32). These concentrations did not exceed the maximum limits set by European legislation (Commission Regulation (EC) No. 1881/2006) for the intake of these marine species. Accumulation of toxic elements tends to be seen in the liver (As (7.31-26.77), Cd (0.11-8.59), Cr (0.21-2.94), Cu (2.64-16.90), Ni (0.16-1.03), Pb (0.0-0.99)). As was the element at highest risk in this Mediterranean region, especially due to red mullet values in muscle. The high As contents with living habits as benthic species that feed near the coast. HMs, especially muscle Cd contents, were associated with higher contents of lipids and organic matter, and bigger specimen size (length and weight), while As was linked to higher fish protein content. However, these relationships between potentially toxic elements (PTE) and biometric indices and body composition parameters depend on species. Finally, the THQ indices indicated that eating fish from Almería Bay poses no human health risk despite pollution from the Almería coastline.

Anaerobic digestion of residues from production and refining of vegetable oils as an alternative to conventional solutions.

The purpose of this work was to study the anaerobic digestion of by-products generated during the production and refining of oil with the objective of proposing an alternative solution (methanisation) to the conventional solutions while reducing the energy consumption of fossil origin on refinery sites. The production of sunflower oil was taken as example. Glycerine from the production of biodiesel was also included in this study. The results show that glycerine has a high potential for methanisation because of its high methane potential (465 ml CH4/g VS) and high metabolization rates (0.42 g VS/g VSS.d). The use of oil cake as substrate for anaerobic digestion is not interesting because it has a low methane potential of 215 ml CH4/g VS only and because it is easily recovered in animal feed. Six residues have quite a high methane potential (465 to 850 ml CH4/g VS) indicating a good potential for anaerobic digestion. However, they contain a mixture of rapidly and slowly biodegradable organic matter and the loading rates must remain quite low (0.03 to 0.09 g VS/g VSS.d) to prevent any accumulation of slowly biodegradable solids in the digesters.

Experimental and modeling investigations of a hybrid upflow anaerobic sludge-filter bed (UASFB) reactor.

A 9.8-L hybrid UASFB reactor, in which the lower half was occupied by a sludge blanket and the upper half by small floating polyethylene media, was evaluated using wine distillery vinasse as substrate. The reactor was operated for a total period of 232 days at 33 + 1 degrees C. Continuous feeding of the reactor was started with an initial OLR of 2.9 g COD/L.d and then it was increased step wise to 19.5 g COD/L.d by increasing the feed COD, while maintaining a constant HRT (1.05 d). The reactor was equipped with a continuous internal recirculation system from top to the bottom at the rate of 9 L/h (upflow velocity = 0.83 m/h) upto day 159 and then it was reduced to about half on day 160 onwards. It was observed that the reduced recirculation rate did not affect the performance of the reactor with an average COD(t) and COD(s) removal efficiencies of 82 and 88%, respectively. A maximum gas production rate of 6.7 L CH(4)/L(reactor).d was achieved for the highest OLR applied. The specific activity analysis depicts that the activity of the attached biomass was more than 2 times higher than that of the granular sludge. The efficiency of liquid mixing was good through out this study. The packing medium had a dual role in the retention of the biomass inside the reactor: i.e. entrapment of biomass within the support and filtration of the granular biomass, preventing it from going out of the reactor. ADM1_10 model simulated well the dynamic evolutions of the main variables in the liquid as well as in the gas phases.

Anaerobic digestion of gelatinous water at laboratory and pilot scale and nitrogen inhibition.

The anaerobic digestion of the liquid residue (gelatinous water) coming from the production of fat from animal residue, was studied at laboratory and pilot scale. Biodegradability (>98%) and biogas potential (675 mL of biogas/g of COD(applied)) of this wastewater are very high. However, due to the high content on nitrogen, an inhibition of the anaerobic activity was observed for quite low concentrations of N-NH(3). Dilution of the wastewater and pH regulation in the reactor around 7.3 are the 2 solutions which were investigated to overcome the nitrogen inhibition at industrial scale. These two solutions were validated at laboratory scale in an anaerobic SBR and then onsite at pilot scale in a continuous reactor. A stable anaerobic digestion was observed in both reactors showing that no nitrogen inhibition was obtained when N-NH(3) concentration in the reactor was kept low.

Mercury contents in relation to biometrics and proximal composition and nutritional levels of fish eaten from the Western Mediterranean Sea (Almería bay).

Total liver and muscle mercury, and muscular composition, biometrics and trophic levels, were determined in four species (Mullus surmuletus, Merluccius merluccius, Auxis rochei and Scomber japonicus) of the Mediterranean Sea (Almería Bay, Spain). Mercury levels did not exceed the maximum residue limit, and M. merluccius obtained the highest level in muscle. Considerable variations in Hg content among individuals were observed in non-gregarious species. A positive correlation between Hg and trophic level or length was found in muscle, but not in liver. Organs (liver or muscle) with major Hg accumulation depend on species; muscle in M. merluccius and liver in S. japonicus. The results indicate that Hg levels in fish depend on intra- and interspecies factors that should be taken into account in systems to monitor Hg levels.

Sublethal and chronic effects of reclaimed water on aquatic organisms. Looking for relationships between physico-chemical characterisation and toxic effects.

The use of reclaimed water for irrigation and aquaculture purposes is generally considered a reliable alternative for sustainable water management in regions with water scarcity. Many organic compounds, generally called compounds of emerging concern (CECs), have been detected in reclaimed water, which implies continuous exposure for aquatic organisms. To date no quality criteria have been proposed for this group of compounds. This work aims to assess the acute, sublethal and chronic effects of reclaimed water using two representative organisms of the aquatic compartment; the green alga Chlorella vulgaris and the microcrustacean Daphnia magna. The study comprises the 72 h-algal growth inhibition test, the D. magna feeding bioassay and the D. magna reproduction test. The results highlighted, for the selected characterised compounds, no differences in the concentrations between the different tertiary WWTP treatments, except for the particular case of carbamazepine. Considering seasonality, no differences were observed between the two different sample collection campaigns. The sublethal and chronic effects observed for these samples could not be explained by the lower concentrations found in the chemical characterisation. However, in the majority of cases, dilution of raw reclaimed water reduced the toxic effects of these samples. Several interactions among compounds can affect the mixture's toxicity. Canonical correlation analyses (CCA) were included to explore the potential relationships between the physico-chemical characterisation of reclaimed water and effects on aquatic organisms. The results corroborated the toxic effect of some pharmaceuticals, in particular beta-blockers and antibiotics, on the growth and yield of green algae, as well as inhibition of daphnia reproduction. Thus the CCA methods could help to elucidate the potential relationships between the physico-chemical characterisation and toxic effects by considering all the potential interactions.

Treatment of distillery vinasse in a high rate anaerobic reactor using low density polyethylene supports.

An anaerobic fixed bed reactor, filled with small floating supports of polyethylene material (Bioflow 30) as inert media, was operated for 6 months to treat vinasse (wine residue after distillation). Bioflow 30 has a density of 0.93 and a specific area of 320 m2/m3. The experimental results showed that the efficiency of the reactor in removal of soluble COD was very good with a maximum organic loading rate of more than 30 g of COD/L x d and a COD removal efficiency of more than 80%. Bioflow 30 showed a high capability of biomass retention with 4-6 g of dried solids per support. Thus, at the end of the experiment, the fixed biomass represented 57 g of solids/L of reactor. The visual observation of the supports and the specific activity (0.54 g COD/g solids x d) of the fixed solids, which remained close to the values obtained with suspended biomass, showed that entrapment was playing an important role in the retention of the biomass inside the reactor. It was then possible to operate the reactor with a very high loading rate as the result of the increase of the solids in the reactor and the maintaining of the specific activity. Bioflow 30 is then an excellent support for use in a high rate anaerobic fixed bed.

Characterization of the activated sludge and of the operating conditions of six SBR treating dairy effluent and operated at industrial scale.

The sludge from six SBRs treating dairy effluent and located at same geographical location, in North East of France, were collected to study their characteristic behavior. The six plants were designed and constructed by the same manufacturer and are working under quite similar operating conditions. The objective of the study was to observe if any similarity existed in the characteristics of the sludge collected from the SBRs. The sludge was characterized for morphological properties (filament index, floc size), settling, compressibility, suspended solids (SS) concentration. The sludge from each plant was different from the others in most of the characteristics. One sludge out of six (sludge G) was completely different from the others with a very degraded structure and low discrete settling and compression. This reactor was not working fully satisfactorily with a too high COD at outlet, probably because this SBR was undergoing repetitive overloading linked to a very bad recovery of the whey by the cheese maker. The five other SBRs were working fully satisfactorily but the characteristics of the five sludges were quite different from one sludge to another. The size of the flocs seemed to be the only parameter measured which could be correlated to the settling characteristics of the sludge. The sludge characteristics and the parameter correlations were also compared with that of municipal activated sludge and were found to be very different.

Leachate flush strategies for managing volatile fatty acids accumulation in leach-bed reactors.

In anaerobic leach-bed reactors (LBRs) co-digesting an easily- and a slowly-degradable substrate, the importance of the leachate flush both on extracting volatile fatty acids (VFAs) at the beginning of newly-started batches and on their consumption in mature reactors was tested. Regarding VFA extraction three leachate flush-rate conditions were studied: 0.5, 1 and 2Lkg-1TSd-1. Results showed that increasing the leachate flush-rate during the acidification phase is essential to increase degradation kinetics. After this initial phase, leachate injection is less important and the flush-rate could be reduced. The injection in mature reactors of leachate with an acetic acid concentration of 5 or 10gL-1 showed that for an optimized VFA consumption in LBRs, VFAs should be provided straight after the methane production peak in order to profit from a higher methanogenic activity, and every 6-7h to maintain a high biogas production rate.

Mesophilic anaerobic digestion of several types of spent livestock bedding in a batch leach-bed reactor: substrate characterization and process performance.

Spent animal bedding is a valuable resource for green energy production in rural areas. The properties of six types of spent bedding collected from deep-litter stables, housing either sheeps, goats, horses or cows, were compared and their anaerobic digestion in a batch Leach-Bed Reactor (LBR) was assessed. Spent horse bedding, when compared to all the other types, appeared to differ the most due to a greater amount of straw added to the litter and a more frequent litter change. Total solids content appeared to vary significantly from one bedding type to another, with consequent impact on the methane produced from the raw substrate. However, all the types of spent bedding had similar VS/TS (82.3-88.9)%, a C/N well-suited to anaerobic digestion (20-28, except that of the horse, 42) and their BMPs were in a narrow range (192-239NmLCH4/gVS). The anaerobic digestion in each LBR was stable and the pH always remained higher than 6.6 regardless of the type of bedding. In contrast to all the other substrates, spent goat bedding showed a stronger acidification resulting in a methane production lag phase. Finally, spent bedding of different origins reached, on average, (89±11)% of their BMP after 60days of operation. This means that this waste is well-suited for treatment in LBRs and that this is a promising process to recover energy from dry agricultural waste.

Optimal conditions for flexible methane production in a demand-based operation of biogas plants.

The aim of the presented work was to study the methane production limits and to determine optimal conditions for flexible operation of an anaerobic reactor in order to set up an operational strategy. Punctual overloads were conducted in a laboratory-scale anaerobic reactor with readily biodegradable solid substrates, and the influences of overload intensity, baseload value and substrate used were investigated. A maximal daily value around 1000mL/L of reactor for methane production has been assessed. This value did not evolve significantly during experiment time, and conditioned the persistence of overloads as well as the flexibility margin on the reactor, which ranged from +25% to +140% on daily production. Results highlighted the fact that for a maximum flexibility, low organic loading rates are better to work with on this type of reactors.

Comparison of the mesophilic and thermophilic anaerobic digestion of spent cow bedding in leach-bed reactors.

Anaerobic digestion of spent cow bedding in batch leach-bed reactors (LBRs) was compared in mesophilic and thermophilic conditions for the first time. Results show that the use of thermophilic conditions enhanced only the degradation kinetics of easily-degradable matter during the first days of the digestion, whereas similar methane yields (80% of the Biomethane Potential) were reached after 42days at both temperatures. Therefore, the anaerobic digestion in LBRs of spent cow bedding, a substrate rich in slowly-degradable compounds, was not improved in term of methane production considering the overall digestion time. Moreover, the high initial biogas production rate in thermophilic reactors was found to significantly reduce the energetic performance of the cogeneration unit at industrial scale, leading to a 5.9% decrease in the annual electricity production when compared to a mesophilic one.

Anaerobic digestion of tannery soak liquor with an aerobic post-treatment.

The leather industry occupies a place of prominence in the Indian economy due to its massive potential for employment, growth and exports. The potential environmental impact of tanning is significant. This study focuses on tannery soak liquor, generated by the soaking of hides and skins, which is characterised by high organic load and high salinity. For these reasons, the soak liquor should be segregated and pre-treated separately before being mixed with the composite wastewater, made of all other streams mixed together. The anaerobic digestion of tannery soak liquor was studied using a UASB. COD removal reached 78% at an OLR of 0.5 kg COD m(-3) d(-1), a HRT of 5 days and a TDS concentration of 71 gl(-1). The combination of the UASB with an aerobic post-treatment enhanced the performance of the overall wastewater treatment process and the COD removal efficiency of the combined anaerobic/aerobic treatment system reached 96%. However, for effective operation, the system had to be operated at very low OLRs, which affects the economic viability of such a process.

Halophilic biological treatment of tannery soak liquor in a sequencing batch reactor.

Hypersaline wastewater (i.e. wastewater containing more than 35 gl(-1) total dissolved solids (TDS)) is generated by various industrial activities. This wastewater, rich in both organic matter and TDS, is difficult to treat using conventional biological wastewater treatment processes. Among the industries generating hypersaline effluents, tanneries are prominent in India. In this study, tannery wastewater from soak pit was treated in a lab-scale SBR for the removal of organic matter. The characterisation of the soak liquor showed that this effluent is biodegradable, though not easily, and highly variable, depending on the origin and the nature of the hides. TDS was in the range of 21-57 gl(-1) and COD was in the range of 1.5-3.6 gl(-1). This soak liquor was biologically treated in an aerobic sequencing batch reactor seeded with halophilic bacteria, and the performance of the system was evaluated under different operating conditions with changes in hydraulic retention time, organic loading rate and salt concentration. The changes in salinity appeared to affect the removal of organic matter more than the changes in hydraulic retention time or organic loading rate. Despite the variations in the characteristics of the soak liquor, the reactor achieved proper removal of organic matter, once the acclimation of the microorganisms was achieved. Optimum removal efficiencies of 95%, 93%, 96% and 92% on COD, PO4 3-, TKN and SS, respectively, could be reached with 5 days hydraulic retention time (HRT), an organic loading rate (OLR) of 0.6 kg COD m(-3)d(-1) and 34 g NaCl l(-1). The organisms responsible for nitrogen removal appeared to be the most sensitive to the modifications of these parameters.

The SBR process: an efficient and economic solution for the treatment of wastewater at small cheesemaking dairies in the Jura mountains.

The small cheesemaking plants in the Jura Mountains (N.E. France) need self-contained solutions for treating their wastewater. Any solution must suit the characteristics of the effluent produced by these small production units and be simple, robust and financially feasible in regard to both capital and running costs. Given this context, a technique based on an SBR was recommended and the operations of the first treatment plant established on an industrial scale, monitored for the first year, with particular attention paid to operating constraints. The results obtained show that the SBR is, from a technical point of view, perfectly adapted to treating cheese production wastewater, with purification levels at 97.7% for total COD and 99.8% for BOD5. In the course of this study, it has been shown that the SBR process, thanks to its simple design and operation, can easily be run by the cheesemaker who will need to devote a minimum of time to it. Furthermore, with treatment costs of around 2 centimes (0.33 US cent) per litre of milk delivered, the SBR process meets perfectly both the technical and financial conditions for treatment as laid down by the Federation of Cooperatives of the Doubs and Jura départements.

High COD wastewater treatment in an aerobic SBR: treatment of effluent from a small farm goat's cheese dairy.

In France, small goat's cheese dairies using traditional craft methods often have no profitable solution for dealing with the whey byproduct of their cheesemaking activity: it is usually mixed with the cleaning wastewater which, in the absence of other possibilities, is then discharged directly into the environment. The volume of such wastewater is small but it has a high COD of around 12-15 g/L. An aerobic SBR was proposed as a method for treating the mixture of wastewater and whey and the first installation was set up on a farm with 170 goats. Its operations were monitored for 7.5 months, particularly in order to measure any excess volume of sludge and to check that such excess remained within acceptable limits, given the high COD of the effluent requiring treatment. The results obtained show that the treated wastewater was of excellent quality, well within the most rigorous discharge norms. With this type of wastewater, excess sludge was produced in only very low amounts with 0.2 g of SS/g of COD. Moreover, the sludge proved to be quick settling which made it possible to: i) maintain a high level of SS in the reactor (up to 15 g/L); ii) withdraw sludge with concentrations reaching 30 g/L after 2 hours of settling. This resulted in a low volume of excess sludge (less than 5% of treated volume), making such aerobic biological treatment in an SBR competitive when compared to the straightforward spreading of all the wastewater.

Use of an anaerobic sequencing batch reactor for parameter estimation in modelling of anaerobic digestion.

The model structure in anaerobic digestion has been clarified following publication of the IWA Anaerobic Digestion Model No. 1 (ADM1). However, parameter values are not well known, and uncertainty and variability in the parameter values given is almost unknown. Additionally, platforms for identification of parameters, namely continuous-flow laboratory digesters, and batch tests suffer from disadvantages such as long run times, and difficulty in defining initial conditions, respectively. Anaerobic sequencing batch reactors (ASBRs) are sequenced into fill-react-settle-decant phases, and offer promising possibilities for estimation of parameters, as they are by nature, dynamic in behaviour, and allow repeatable behaviour to establish initial conditions, and evaluate parameters. In this study, we estimated parameters describing winery wastewater (most COD as ethanol) degradation using data from sequencing operation, and validated these parameters using unsequenced pulses of ethanol and acetate. The model used was the ADM1, with an extension for ethanol degradation. Parameter confidence spaces were found by non-linear, correlated analysis of the two main Monod parameters; maximum uptake rate (k(m)), and half saturation concentration (K(S)). These parameters could be estimated together using only the measured acetate concentration (20 points per cycle). From interpolating the single cycle acetate data to multiple cycles, we estimate that a practical "optimal" identifiability could be achieved after two cycles for the acetate parameters, and three cycles for the ethanol parameters. The parameters found performed well in the short term, and represented the pulses of acetate and ethanol (within 4 days of the winery-fed cycles) very well. The main discrepancy was poor prediction of pH dynamics, which could be due to an unidentified buffer with an overall influence the same as a weak base (possibly CaCO3). Based on this work, ASBR systems are effective for parameter estimation, especially for comparative wastewater characterisation. The main disadvantages are heavy computational requirements for multiple cycles, and difficulty in establishing the correct biomass concentration in the reactor, though the last is also a disadvantage for continuous fixed film reactors, and especially, batch tests.

The anaerobic SBR process: basic principles for design and automation.

This study has determined the purification performance and the basic principles for the design of an anaerobic SBR (ASBR) to be used to treat wastewater generated in the food industries. Two ASBR's were set up and one fed with a slaughterhouse effluent at low concentration, the other with concentrated dairy wastewater. The maximum loading rate applied should not exceed 4.5 g of COD/L/day for the dilute effluent and 6 g of COD/L/day for the concentrated effluent. At higher loading rates, the reactors become difficult to operate, mainly because of sludge removal problems, and purification efficiency declines. A detailed study of the kinetics (TOC, VFA, rate of biogas production) throughout one treatment cycle led to the development of a simple control strategy based on the monitoring of the biogas production rate which was then applied to the reactor treating the dairy wastewater. After automation, the reactor worked free of problems at an average pollution load of 5.4 g of COD/L/day.