E. Sánchez

Anaerobic treatment of palm oil mill effluent in a two stage up-flow anaerobic sludge blanket (UASB) system

A high rate anaerobic treatment of palm oil mill effluent (POME) was achieved in a two-stage up-flow anaerobic sludge blanket (UASB) reactor. The acidogenic reactor acclimated rapidly to the wastewater and was tolerant to a suspended solids (SS) concentration of 5.4 g l?1 in the influent wastewater. Loading was gradually increased over a period of 100 days resulting in a satisfactory hydrolysis and acidification giving a maximum rate of acid production of 4.1 g l?1 d?1 acetic acid at a loading rate of 16.6 g l?1 d?1 COD at a hydraulic retention time of 0.9 days. An increase in alkalinity throughout the acclimatization maintained the effluent from the reactor at around pH 5.8. The methanogenic reactor was initially fed on dilutions of the effluent from the first stage reactor after pH adjustment. The loading was gradually increased, and then stepwise, to 60 g l?1 d?1 COD at which point COD removal efficiency had declined significantly and an accumulation of long-chain volatile fatty acids was observed. It was concluded that the reactor could work efficiently up to loadings of 30 g 1?1 d?1 COD, whilst producing a good methane yield and a COD reduction of greater than 90%. Effluent recirculation alleviated the need for alkali additions to the feed of the methanogenic reactor and a direct coupling of the two reactors was achieved towards the end of the experimental run of 175 days. Both reactors showed granule formation with distinct morphological characteristics; these were observed to be formed after 80 days in the acidogenic reactor and after 110 days in the methanogenic reactor.

Influence of different natural zeolite concentrations on the anaerobic digestion of piggery waste

The effect of different natural zeolite concentrations on the anaerobic digestion of piggery waste was studied. Natural zeolite doses in the range 0.2-10 g/l of wastewater were used in batch experiments, which were carried out at temperatures between 27 degrees C and 30 degrees C. Total chemical oxygen demand (COD), total and volatile solids, ammonia and organic nitrogen, pH, total volatile fatty acids (TVFA), alkalinity (Alk) and accumulative methane production were determined during 30 days of digestion. The anaerobic digestion process was favored by the addition of natural zeolite at doses between 2 and 4 g/l and increasingly inhibited at doses beyond 6 g/l. A first-order kinetic model of COD removal was used to determine the apparent kinetic constants of the process. The kinetic constant values increased with the zeolite amount up to a concentration of 4 g/l. The values of the maximum accumulative methane production (Gm) increased until zeolite concentrations of 2-4 g/l. The addition of zeolite reduced the values of the TVFA/ Alk ratio while increasing the pH values, and these facts could contribute to the process failure at zeolite doses of 10 g/l.

Heavy metals removal from acid mine drainage water using biogenic hydrogen sulphide and effluent from anaerobic treatment: Effect of pH

Four alternatives (runs A, B, C and D) for heavy metals removal (Fe, Cu, Zn and Al) from acid mine drainage water (AMDW) produced in the mining areas of the Huelva Province, Spain, were evaluated. In run A, the anaerobic effluent from the treatment of acid mine drainage water (cheese whey added as a source of carbon) was mixed with the raw AMDW. The pH increased to 3.5 with the addition of KOH. In run B, biogas with around 30% of hydrogen sulphide obtained in the anaerobic reactor was sparged to the mixture obtained in run A, but in this case at a pH of 5.5. In run C, the pH of the raw AMDW was increased to 3.5 by the addition of KOH solution. Finally, in run D, the pH of the raw AMDW was increased to 5.5 by the addition of KOH solution and further biogas was sparged under the same conditions as in run A. It was found that heavy metal removal was a function of pH. At a pH of 3.5 most of the iron was removed while Zn and Cu were partially removed. At a pH of 5.5 the removal of all metals increased considerably. The best results were obtained in run B where the percentages of removal of Fe, Cu, Zn and Al achieved values of 91.3, 96.1, 79.0 and 99.0%, respectively. According to the experimental results obtained tentative schemas of the flow diagram of the processes were proposed.

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time.

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.

Assessment of a microalgae pond for post-treatment of the effluent from an anaerobic fixed bed reactor treating distillery wastewater

Abstract An evaluation of the performance of a laboratory‐scale microalgae pond treating effluent from an anaerobic fixed bed reactor digesting distillery wastewater was carried out. The microalgae pond operated with an effluent recycling (R) of 10:1 with respect to the influent and at surface organic loading rates of 418 kg COD ha−1 day−1 and 92 kg BOD5 ha−1 day−1. During the experiment total chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total solids (TS), total suspended solids (TSS), volatile suspended solids (VSS), total nitrogen, ammonia, total phosphorus, orthophosphate, total chlorophyll (C T) and chlorophyll a (C a ) concentrations were monitored. Overall COD and BOD5 removal efficiencies of 98.2 % and 98.8 % were obtained. The global solids removal efficiencies were of 93.2%, 92.6 % and 97.6 % for TS, TSS and VSS, respectively. The removal efficiencies obtained for organic nitrogen and ammonia were 90.2% and 84.1%, respectively. Finally, the removals for total phosphorus and orthophosphate were 85.5% and 87.3%, respectively. It was demonstrated that microalgae grew in this waste by determination of the total chlorophyll and chlorophyll a in the effluent.

The impact of ammonia nitrogen concentration and zeolite addition on the specific methanogenic activity of granular and flocculent anaerobic sludges.

This work presents the effect of ammonia nitrogen concentration and zeolite addition on the specific methanogenic activity (SMA) of different anaerobic sludges with various physical structures (granular and flocculent), operating in batch conditions. Piggery, malting production and urban sludges derived from full-scale anaerobic reactors were tested in the experiment as the source of inoculum in batch digesters. It was found that piggery sludge was the most affected by the increase of ammonia nitrogen concentration while malting producing and municipal sludges were less affected. In general, the addition of zeolite at doses in the range of 0.01–0.1 g/g VSS reduced the inhibitory effect of N-NH4 + for piggery sludge (P.S.). For this sludge, the propionic:acetic ratio increased when the concentration of N-NH4 + increased, indicating that methanogenesis was affected. Finally, a study of the microbial population involved in this study for P.S. by using 16S rRNA based molecular techniques revealed a presence of microorganisms following the order: Methanococcaceae > Methanosarcina > Methanosaeta.

Production of biomass (algae-bacteria) by using a mixture of settled swine and sewage as substrate

This paper presents the use of a mixture of settled swine and sewage as substrate for biomass production, mainly constituted by microalgae Chlorella vulgaris and aerobic bacteria, growing outdoor at different dilution rates in a continuous mode. The experiments were carried out in 16-litre volume laboratory ponds operating at hydraulic retention times (HRT) in a range of 4–14 days equivalent to dilution rates (D) in a range of 0.250–0.071 d−1. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total biochemical oxygen demand (TBOD5), total suspended solids (TSS), volatile suspended solids (VSS), total Chlorophyll (Σ C), total Kjeldahl nitrogen (TKN), ammonia nitrogen, total phosphorous, orthophosphate and pH were monitored. An empirical relationship between the dilution rate (D) and the removal efficiencies of TCOD, SCOD, TBOD5, TKN and total phosphorous was found. The occurrence of an inhibition process for TCOD, TBOD5, TKN and total phosphorous removals was observed. The Andrews kinetic model was successfully applied to these experimental data, while the Monod model was more suitable for studying the variation of the SCOD removal rate with the effluent SCOD concentration. The maximum microalgal biomass productivity was found to be in the range of 93–98 mg VSSA/L d (37.2–39.2 g/m2d) at dilution rates in the range of 0.167–0.250 d−1, where VSSA is the concentration of microalgae expressed in VSS. In the case of the bacteria, the productivity increased linearly with the dilution rate being maximum at a D value of 0.25 d−1. It was concluded that the mixture of pre-treated swine and sewage used as substrate, contributed to the obtention of a high biomass (microalgae-bacteria) production, providing a simple technology feasible to be applied in developing countries.

Effect of ionic exchanger addition on the anaerobic digestion of cow manure

Abstract The long retention time required for cow manure digestion could be attributed to the presence of complex organic compounds but also, to the high concentration of ammonia (NH4 + plus free NH3) that affects the anaerobic digestion. Both problems could be ameliorated by the utilization of ionic exchanger supports. The subject of the present work was the evaluation of the natural zeolite as ionic exchanger. It was observed that the digester with zeolite addition had the best behaviour during the experiments while inhibition of anaerobic degradation was obtained in a control digester with suspended biomass.

Influence of heavy metal supplementation on specific methanogenic activity and microbial communities detected in batch anaerobic digesters

Natural and modified zeolites (0.5–1.0 mm) from the Tasajera deposit in Cuba were used to enhance the anaerobic digestion process of synthetic substrates. Natural zeolites were modified by ionic exchange and by adsorption with nickel, cobalt and magnesium. The experiments were carried out by using an inoculum from a full-scale anaerobic reactor treating winery wastewater. Modified natural zeolites not only enhanced the anaerobic digestion process, but also increased the specific methanogenic activity (SMA) of the sludges. The textural and chemical surface characteristics of the modified zeolites were related to the process performance, volatile fatty acid (VFA) production and microbial communities found in the digesters. For the selected dose of modified zeolites [0.05 g/g of volatile suspended solids (VSS)], the lowest concentration was found for cobalt followed by nickel and magnesium. Based on the analyses of anaerobic biofilms, the heavy metal incorporated into the zeolite was shown to have a great influence on the predominance of species. For example, the presence of nickel and cobalt favoured Methanosaeta, while at the same dose magnesic zeolite stimulated the presence of Methanosarcina and sulfate-reducing bacteria (SRB). In digesters with modified zeolites and metal supplementations the values of SMA were higher than those obtained in the control and natural zeolite digesters.

Kinetic evaluation of the psychrophylic anaerobic digestion of synthetic domestic sewage using an upflow filter

A study of the anaerobic digestion process of synthetic domestic sewage (total COD: 705 mg/L) was carried out. The digestion was conducted in an upflow anaerobic filter with corrugated plastic rings as packing media at psychrophilic temperature (15-17 degrees C). For HRTs of between 10.0 and 17.1h, the total COD removal efficiency was almost constant and independent on the HRT, achieving an average value of around 80%. However, when the HRT decreased from 7.0 to 3.2h the efficiency diminished from 77% to 65%. This decrease in removal efficiency was parallel to the increase in the VFA/Alkalinity ratio for this HRT range. The flow pattern observed in the reactor studied was intermediate between plug-flow and CSTR systems, although the plug-flow was predominant. It can also be observed that Young and McCartys model almost coincided with the CSTR model, when the biodegradable COD was used for fitting the data. The Manariotis equation allowed a better fit of the experimental data (total COD removal efficiency with influent substrate concentration and HRT) than the Young model. The methane yield coefficient obtained was 0.15 L CH(4)/g COD consumed.