Specific Organic Loading Rate Research Articles

Specific Organic Loading Rate Control for Improving Fermentative Hydrogen Production

Inhibiting homoacetogens is one of the main challenges in fermentative hydrogen production because these hydrogen consumers have similar growth features to hydrogen producers. Homoacetogens have been related to the excessive accumulation of biomass in fermentative reactors. Therefore, a suitable food/microorganism ratio has the potential to minimize the homoacetogenic activity. In this work, the specific organic loading rate (SOLR) was controlled in two fermentative fixed-bed up-flow reactors through scheduled biomass discharges. Reactors were differentiated by the bed arrangement, namely, packed and structured conformation. The SOLR decay along the time in both reactors was previously simulated according to the literature data. The volume and volatile suspended solids (VSS) concentration of discharges was estimated from the first discharge, and then additional discharges were planned. Biomass discharges removed 21% of the total biomass produced in the reactors, maintaining SOLR values of 3.0 ± 0.4 and 3.9 ± 0.5 g sucrose g−1 VSS d−1 in the packed-bed and structured-bed reactors, respectively. Such a control of the SOLR enabled continuous and stable hydrogen production at 2.2 ± 0.2 L H2 L−1 d−1 in the packed-bed reactor and 1.0 ± 0.3 L H2 L−1 d−1 in the structured-bed one. Controlling biomass was demonstrated to be a suitable strategy for keeping the continuous hydrogen production, although the fermentative activity was impaired in the structured-bed reactor. The homoacetogenic was partially inhibited, accounting for no more than 30% of the total acetic acid produced in the reactor. Overall, the high amount of attached biomass in the packed-bed reactor provided more robustness to the system, offsetting the periodic suspended biomass losses via the planned discharges. Better characterizing both the VSS composition (aiming to differentiate cells from polymeric substances) and the bed hydrodynamics could be useful to optimize the online SOLR control.

ORGANIC REMOVAL IN DOMESTIC WASTEWATER USING ANAEROBIC TREATMENT SYSTEM-MBBR WITH FLOW RECIRCULATION RATIO AND INTERMITTENT AERATION

Aim: The modified Small-scale Domestic Sewage Treatment Plant (SDSTP) reactor with anaerobic fixed bed- aerobic Moving Bed Biofilm Reactor (MBBR) is implemented to find the optimum condition for organic degradation related to recirculation and intermittent aeration practices with the purpose to comply with the governmental regulation standard.  Methodology and Results: This research have been done with the artificial wastewater with characteristic similar to the sewage treatment plant (STP) of Telkom company with ratio C:N:P of characterized domestic wastewater is 252.40:85.42:3.01 that consists of glucose, NH4Cl, potassium dihydrogen phosphate, potassium nitrate, and sodium nitrite (NaNO2). Reactor design related with attached biomass in media until 2478.56 mg MLVSS.L-1 with the growth kinetics rate (μ) of 0.4691 day—1. The artificial wastewater is applied the determine the optimum variation of flow recirculation and periodic aeration in specific Hydraulics Retention Time (HRT) and Organic Loading Rate (OLR). In this research, the optimum recirculation ratio for organic degradation is 26.40 L.h-1 and the optimum aeration frequency variation is  12 hours in intermittent frequency with the maximum efficiency of organic degradation of 76.10% with the degradation efficiency real domestic wastewater application from STP Telkom company is 83.09%. Conclusion, significance and impact study:  Stover-Kincannon model is the best model with highest accuracy rate to model the degradation performance of organic compounds by the anaerobic fixed bed- aerobic MBBR SDSTP with determination coefficient 0.8623 and also degradation coefficient 38.121 day-1 compared with other models studied in this research.

Enrichment of thermophilic methanogenic microflora from mesophilic waste activated sludge for anaerobic digestion of garbage slurry

This study investigated a startup strategy for thermophilic methanogenic enrichment. Conventional waste activated sludge (WAS) was used as the seed. The WAS seed was incubated at 55°C in a continuous-flow stirred tank reactor, with garbage slurry fed continuously as a substrate. One of the two reactors (termed reactor-high, RH) was fed with a high concentration of substrate (30g-COD/L), while the other (reactor-low, RL) received a lower concentration of feed (15g-COD/L). The specific organic loading rate was 0.2g-COD/L/day initially, which was gradually increased by shortening the hydraulic retention time. The final OLR was 3.2g-COD/L/day, after more than 90% of the initial WAS got washed out from the reactor and thermophilic microorganisms became dominant in the reactors. Biogas production rate and methane conversion ratio depended on substrate concentration, although total chemical oxygen demand removal and methane content were almost the same in RH and RL. Biogas production rate in RH was 3.2 times higher than that in RL, while the conversion ratio of RH was 1.6 times higher than that of RL. Quantitative polymerase chain reaction analysis using specific primers for the mcrA gene and high-throughput sequencing analysis of 16S rRNA gene amplicons demonstrated post enrichment differences in the microbial community, relative to that in the WAS. There was no significant difference in the enriched microbial community composition between RH and RL. In conclusion, thermophilic methanogenic microflora can be enriched from mesophilic seeds. Methanothermobacter, Methanosarcina, and other thermophilic bacteria were enriched in the community over time, with these thermophiles collectively accounting for ∼80% of the stable thermophilic community.

Ultrasound-assisted digestate treatment of manure digestate for increased biogas production in small pilot scale anaerobic digesters

In this study, ultrasound (US) disintegration was evaluated as a digestate treatment strategy. Digestate treatment is the physical, chemical or biological treatment and recirculation AD of the effluents of the anaerobic digesters (i.e., digestate) to the digester as supplementary feed to increase their utilization potential for energy conversion or green chemical production in post-valorization pathways. In this scope, semi-continuous small pilot scale manure digesters were operated in parallel with various operational settings. One of the digesters was fed by adding disintegrated digestate to an equal volume of fresh manure feed (recycle ratio of 1). The obtained results showed that US-assisted digestate treatment at 1500 kJ/kg TS specific energy input with 30 days of hydraulic retention time increased the methane production rate by 18%. The increased methane production rate was found to be related to the applied specific energy and organic loading rate. A basic cost-benefit analysis showed that the energy demand of the US disintegration at lab scale was higher than the energy that can be recovered from the additional biogas produced.

Strategies to improve the biohydrogen production from cassava wastewater in fixed-bed reactors

The biological production of hydrogen from cassava starch wastewater (CSW) was evaluated in an anaerobic fixed-bed reactor (UAFBR). The assays were carried out to evaluate the effects of organic loading rate (OLR) increase and strategies of inoculation (AS – anaerobic sludge thermally treated and NF – naturally fermented cassava starch wastewater) on UAFBR performance. The OLR increase (10–20 g L−1 d−1) associated with hydraulic retention time (HRT) decrease (4–2 h) improved the volumetric hydrogen production rate (VHPR, from 229 to 550 mLH2.L−1.d−1), molar hydrogen flow rate (MHFR, from 1.0 to 2.5 mmolH2.h−1) and hydrogen yield (HY, from 0.2 to 0.3 molH2.mol−1Carb) from CSW due to increase in substrate availability. Both inoculation alternatives (AS and NF) were effective for the selection of acidogenic microorganisms, which demonstrates that NF could be considered a simple and economic alternative for the acquisition of inoculum for continuous acidogenic reactors. Hydrogen production decreased after 10 days of operation when the specific organic loading rate (SOLR) reached reduced values (<1 gCarb.g−1VSS.d−1), which impairs hydrogen production. For all assays, methane was present in the biogas after the 20th day of operation mainly due to biomass accumulation, which alters the biota of the reactor. Although many factors could influence the process performance in UAFBR for the production of biohydrogen, the accumulation of biomass have been pointed as the main factor in the determination of the production time, thus demanding the implementation of systematic practices to remove the excess of biomass to maintain the SOLR in levels adequate for hydrogen production.

Strategies of anaerobic sludge granulation in an EGSB reactor

Anaerobic sludge granulation was evaluated in an expanded granular sludge bed (EGSB) reactor based on the increases in the specific organic loading rate (SOLR). The effect of precursor substances (calcium chloride, sodium chloride, and tannin) on the development of granular sludge was also investigated in batch reactors. The reactors were fed with synthetic sewage and operated in mesophilic conditions. The EGSB was operated with a variable hydraulic retention time (HRT) and the batch reactors, with cycles of 8 h and 16 h. The increase of SOLR from 17.4 ± 7.4 to 104.6 ± 66.7 mgCOD gVSS-1 d-1 in the EGSB resulted in an increase on the average granules diameter from 344.3 to 1583.3 μm. These conditions also favored the reduction rates of chemical oxygen demand (COD) and volatile fatty acids (VFAs) concentration in the reactor. When the upflow velocity suffered an abrupt increase (from 0.06 L h-1 to 0.25 L h-1), the granules size began to decrease and lose their settleability characteristics. Considering this, it is proposed to start the biomass granulation process without effluent recirculation, and, after the granules reach the desired size and settleability capacity, the normal operation of EGSB reactor starts. The results showed that calcium chloride was more efficient for granulation. CaCl2 addition can be performed only during the reactor's start-up, improving granulation and reducing start-up time. Thus, these results have practical implications as granules maintenance is the key to the proper EGSB operation.

Evaluation of anionic surfactant removal by anaerobic degradation of commercial laundry wastewater and domestic sewage

ABSTRACTAn expanded granular sludge bed reactor was evaluated for the anaerobic digestion of commercial laundry wastewater and domestic sewage focused on the removal of linear alkylbenzene sulfonate (LAS). The reactor was operated in three stages, all under mesophilic conditions and with a hydraulic retention time of 36 h. At stage I, the laundry wastewater was diluted with tap water (influent: 15.3 ± 4.9 mg LAS/L); at stage II, 50% of the feed volume was domestic sewage and 50% was a mixture of tap water and laundry wastewater (influent: 15.8 ± 4.9 mg LAS/L); and at stage III, only domestic sewage was used as a diluent of the laundry wastewater (influent: 24.1 ± 4.1 mg LAS/L). Due to the addition of domestic sewage the organic compounds content and LAS in the influent increased. Under such conditions, it was observed that LAS removal rate decreased from 77.2 ± 14.9% (stage I) to 55.3 ± 18.4% (stage III). Statistical tests indicated that the decrease of the LAS removal rate was significant and indicated a correlation between the removal of LAS and specific organic loading rate. The analysis of 16S rRNA gene sequencing revealed genera similar to Geobacter, Desulfovibrio, Syntrophomonas, Syntrophus, Desulfobulbus, Desulfomonile, and Desulfomicrobium, which were related to the degradation of LAS.

Organic matter capture by a high-rate inoculum-chemostat and MBBR system

The main objective of this study was to develop an innovative process to maximize the bio-transformation of colloidal and soluble biodegradable matter (CSB) into particulate matter (XB) for energy recovery via methane production. Two configurations were studied: (1) high-rate moving bed bioreactor (HR-MBBR) and (2) inoculum-chemostat (IC) system consisting of a very HR-MBBR inoculating a continuous flow stirred-tank reactor. The effect of hydraulic retention time (HRT), specific organic loading rate (SOLR), and dissolved oxygen (DO) level were determined using real wastewater at pilot scale. Results showed that in the HR-MBBR process, a very high CSB bio-transformation efficiency (90%) was obtained in a wide range of SOLRs (2.0 to 5.5 g CSB m−2 d−1) corresponding to an optimum HRT of 36 minutes. The IC process reached a maximum CSB bio-transformation efficiency of 77%, at SOLRs ranging from 22 to 30 g CSB m−2 d−1 at an HRT of 3.7 hours. The DO concentration in the HR-MBBR influenced the CSB bio-transformation ratio, while the HRT and the SOLR were the dominant factors influencing this ratio in the IC process. Based on these results, the IC process could be an interesting alternative to high-rate systems towards obtaining energy positive/efficient from water resource recovery facilities.

Greywater treatment in an aerobic SBR: sludge structure and kinetics.

In order to have an efficient operation, sequencing batch reactors (SBR) must support granular biomass with high conversion rates, settling properties, and be able to deal with the inherent variability of the composition of real wastewaters. In this study, the effect of the influent composition and the specific organic loading rate (Bx) on the granulation process was evaluated in two SBRs, fed with greywater (GW) and a synthetic medium (SM). The feeding with SM led to the formation of compact granular biomass, with a sludge volume index (SVI) of 22.4 mL g-1, and a zone settling velocity (ZSV) of 13.1 m h-1. In contrast, feeding with GW induced the formation of filamentous granules, with lower settling properties (SVI = 165 mL g-1 and ZSV = 10 m h-1), when the system was operated at high Bx (4.4 kg COD kg VSS-1 d-1). However, the reduction of the average Bx to 2 kg COD kg VSS-1 d-1 induced an improvement in the morphology and properties of the granules (SVI = 98 mL g-1 and ZSV = 13 m h-1). Furthermore, the kinetic analysis indicated that granules cultivated with SM were formed by fast growing microorganisms with a high cell yield, whereas those cultivated in GW presented a much lower cell yield.

Calcium dosing for the simultaneous control of biomass retention and the enhancement of fermentative biohydrogen production in an innovative fixed-film bioreactor

Biohydrogen (bioH2) production via dark fermentation is an attractive approach to overcome the drawbacks of conventional hydrogen production methods and represents a preliminary alternative for the management of organic wastes. Fundamental studies are still required to enhance the performance of bioH2 production systems, with emphasis on the development of novel reactor configurations. The anaerobic structured-bed reactor (ASTBR) is a recently developed configuration with great potential for bioH2 production, although operating strategies are still required to minimize biomass washout in such systems. In this context, calcium dosing has been investigated as a strategy to enhance both biomass retention and bioH2 production rates in the ASTBR. The present study employed varying COD/calcium ratios (4423, 2079, 1357, 1012, 884, and 632) in continuous experiments under mesophilic conditions (25 °C). Calcium dosing effectively enhanced biomass retention within the ASTBR, directly increasing the availability of metabolic energy for different metabolic pathways rather than cell synthesis. An optimal COD/calcium ratio of 1360 was mathematically estimated for bioH2 production, which is consistent with the results obtained experimentally. The specific organic loading rate (SOLR) was better controlled at this ratio, indicating the establishment of balanced conditions in terms of substrate availability and biomass concentration. Conversely, bioH2 production was severely impaired at COD/calcium values below and above the optimal range, most likely due to enhancement of the homoacetogenic pathway as a result of unbalanced conditions in the SOLR. Furthermore, biomass accumulation did not strongly affect the mean residence time of the ASTBR, facilitating its robust and enhanced solid retention.

Influence of sludge age on the performance of MFC treating winery wastewater

The objective of this paper was to determine the influence of sludge age on microbial fuel cell (MFC) performance for generating electricity and removing organic matter from winery wastewater. Six Solid Retention Times (SRT) were used: 1.2, 1.4, 1.8, 2.3, 3.5 and 7.0 d. Results demonstrate that the electricity generation increases by decreasing the SRT, selecting electrogenic microorganisms, once the specific organic loading rate (SOLR) increased and the competition for substrate was reduced. Decreasing the SRT, coulombic efficiency can be increased from 3.4% to almost 42.2% and maximum power density from 58 to 890 mW m−2. However the SRT did not influence on organic matter removal in biological treatment, because only a small part of COD was removed oscillating around 600 mg L−1 d−1and it was very similar at all SRT studied.

Operational strategies for long-term biohydrogen production from sugarcane stillage in a continuous acidogenic packed-bed reactor

The use of packed-bed reactors for biohydrogen production often results in performance losses in the short term because of the negative effects of operational factors, such as biomass accumulation and inadequate pH conditions. Because packed-bed systems constitute a promising technology for biohydrogen production, studies on continuous hydrogen production over the long term must be carefully conducted by applying proper operational strategies. Therefore, this study assessed continuous biohydrogen production in a packed-bed reactor operated under thermophilic conditions (55 °C) using sugarcane stillage as the substrate. The results indicated that the acidogenic reactor presented a capacity for recovering from performance losses, regardless of their cause, and maintaining continuous hydrogen production rates under long-term operation (240 days). pH proved to be a key factor for obtaining continuous hydrogen production, and the optimal results were observed in a pH range from 5.1 to 5.2. Furthermore, an optimal specific organic loading rate of 6.3–6.4 g carbohydrates g−1 volatile suspended solids d−1 was observed, and this value is consistent with the results of previous studies focused on hydrogen production from fermentative systems.

Start-up and operation of an AnMBR for winery wastewater treatment

A sidestream anaerobic membrane bioreactor (AnMBR) was started up and operated under organic load oscillations in order to determine its feasibility for winery wastewater treatment. The stable operation was assured by keeping a ratio between intermediate alkalinity and total alkalinity below 0.4 and the specific organic loading rate below the methanogenic activity (0.3kgCODkgMLSS−1d−1) achieving a 96.7±2.7% chemical oxygen demand (COD) removal efficiency. The maximum organic loading rate (OLR) achieved was 3.4kgCODm−3d−1. The biogas production varied according with the OLR that was on average 0.50±0.17m3biogasm−3digesterd−1 with an 87.1±3.0% of methane. The external membrane module reached a flux of 20.2±8.5LMH operating at a mixed liquor suspended solids concentration of 4.78±1.9gL−1 and a crossflow velocity of 0.64ms−1. The crossflow velocity helped to remove the cake layer attached on the membrane that was the main contribution (>80%) to flux decline. The energy balance of the AnMBR revealed that a sidestream configuration would be a feasible option during vintage season.

The application of an innovative continuous multiple tube reactor as a strategy to control the specific organic loading rate for biohydrogen production by dark fermentation

Biohydrogen production in fixed-bed reactors often leads to unstable and decreasing patterns because the excessive accumulation of biomass in the bed negatively affects the specific organic loading rate (SOLR) applied to the reactor. In this context, an innovative reactor configuration, i.e., the continuous multiple tube reactor (CMTR), was assessed in an attempt to better control the SOLR for biohydrogen production. The CMTR provides a continuous discharge of biomass, preventing the accumulation of solids in the long-term. Sucrose was used as the carbon source and mesophilic temperature conditions (25°C) were applied in three continuous assays. The reactor showed better performance when support material was placed in the outlet chamber to enhance biomass retention within the reactor. Although the SOLR could not be effectively controlled, reaching values usually higher than 10gsucroseg−1VSSd−1, the volumetric hydrogen production and molar hydrogen production rates peaked, respectively, at 1470mLH2L−1d−1 and 45mmolH2d−1, indicating that the CMTR was a suitable configuration for biohydrogen production.

The use of the carbon/nitrogen ratio and specific organic loading rate as tools for improving biohydrogen production in fixed-bed reactors

This study assessed the effect of the carbon/nitrogen (C/N) ratio on the hydrogen production from sucrose-based synthetic wastewater in upflow fixed-bed anaerobic reactors. C/N ratios of 40, 90, 140, and 190 (gC/gN) were studied using sucrose and urea as the carbon and nitrogen sources, respectively. An optimum hydrogen yield of 3.5molH2mol−1 sucrose was obtained for a C/N ratio of 137 by means of mathematical adjustment. For all C/N ratios, the sucrose removal efficiency reached values greater than 80% and was stable after the transient stage. However, biogas production was not stable at all C/N ratios as a consequence of the continuous decreasing of the specific organic loading rate (SOLR) when the biomass accumulated in the fixed-bed, causing the proliferation of H2-consuming microorganisms. It was found that the application of a constant SOLR of 6.0gsucroseg−1VSSd−1 stabilized the system.

Sludge minimization in municipal wastewater treatment by polyhydroxyalkanoate (PHA) production.

An innovative approach has been recently proposed in order to link polyhydroxyalkanoates (PHA) production with sludge minimization in municipal wastewater treatment, where (1) a sequencing batch reactor (SBR) is used for the simultaneous municipal wastewater treatment and the selection/enrichment of biomass with storage ability and (2) the acidogenic fermentation of the primary sludge is used to produce a stream rich in volatile fatty acids (VFAs) as the carbon source for the following PHA accumulation stage. The reliability of the proposed process has been evaluated at lab scale by using substrate synthetic mixtures for both stages, simulating a low-strength municipal wastewater and the effluent from primary sludge fermentation, respectively. Six SBR runs were performed under the same operating conditions, each time starting from a new activated sludge inoculum. In every SBR run, despite the low VFA content (10% chemical oxygen demand, COD basis) of the substrate synthetic mixture, a stable feast-famine regime was established, ensuring the necessary selection/enrichment of the sludge and soluble COD removal to 89%. A good process reproducibility was observed, as also confirmed by denaturing gradient gel electrophoresis (DGGE) analysis of the microbial community, which showed that a high similarity after SBR steady-state had been reached. The main variation factors of the storage properties among different runs were uncontrolled changes of settling properties which in turn caused variations of both sludge retention time and specific organic loading rate. In the following accumulation batch tests, the selected/enriched consortium was able to accumulate PHA with good rate (63 mg CODPHA g CODXa(-1) h(-1)) and yield (0.23 CODPHA CODΔS(-1)) in spite that the feeding solution was different from the acclimation one. Even though the PHA production performance still requires optimization, the proposed process has a good potential especially if coupled to minimization of both primary sludge (by its use as the VFA source for the PHA accumulation, via previous fermentation) and excess secondary sludge (by its use as the biomass source for the PHA accumulation).

Effect of recycle on treatment of aircraft de-icing fluid in an anaerobic baffled reactors

Aircraft de-icing fluid at 7 000 mg COD/&#8467; was successfully treated in an anaerobic baffled reactor operated with and without recycle at volumetric organic loading rate of between 4 and 11 g COD/&#8467;reactor·d. Reactor recycle was found to improve reactor performance. The anaerobic baffled reactor operated with a 6:1 recycle ratio achieved a minimum hydraulic retention time of 17 h with an acceptable COD removal efficiency of 93% at a volumetric organic loading rate of 9.9 g COD/&#8467;reactor·d. This corresponded to a specific organic loading rate of 0.35 g COD/g VSS·d and specific organic removal rate of 0.32 g CODrem/g VSS·d. Without recycle similar removal efficiency was achieved; however, the loading rates were about 40% less. Due to biomass growth specific organic loading rate was not found to vary significantly through most of the experimental period despite loading rate increases. Hydrodynamically, an anaerobic baffled reactor may be characterised as an in-series continuously stirred tank reactor where the number of continuously stirred tank reactors corresponded to the number of actual compartments. Volatile fatty acid profiles tend to indicate that anaerobic baffled reactor compartmentalisation served to separate acidogenic and methanogenic activities longitudinally through the reactor, with the highest proportion of acidogenic activity in the first compartments. The net accumulated yield within the anaerobic baffled reactor was found to be of 0.007 g VSS/g CODrem when the ABR was operated without recycle and of 0.016 g VSS/g CODrem for the ABR operated with recycle. Water SA Vol.31 (3) 2005: pp.377-384

Treatment of settled piggery waste by a down-flow anaerobic fixed bed reactor

A study of the effect of organic volumetric loading rate (B V ) on the performance of a down-flow anaerobic fixed bed reactor (DFAFBR) treating settled piggery waste was carried out at a range of between 1.1 and 6.8 g COD dm -3 d -1 . The reactor operated at good removal efficiencies and stability under the operational conditions studied. Logarithmic empirical equations described adequately the removal efficiency for different parameters studied (COD, SCOD, BOD, TS, VS, TSS, VSS and phosphorous). Although process stability was affected by the increase of B V , process failure was not observed. A logarithmic relationship was found to describe the influence of B V on the TVFA/alkalinity ratio (p). A linear correlation was found between the effluent substrate concentration and the values of p and between p and the CO 2 /CH 4 ratio in the biogas. The effect of the hydraulic volumetric loading rate (H v ) on the flow pattern of the reactor was evaluated. Dispersion number (D n ) was in the range of 0.17-0.37 for the maximum and minimum values of H V studied, respectively. The ratio between the real and theoretical HRT increased as the H V decreased. These results demonstrate that axial dispersion increased as the H V and the Reynolds number decreased. Due to the hydraulic behaviour of the reactor, the kinetic model developed by Lawrence and McCarty was used for describing the experimental results obtained. Maximum specific substrate removal rate (K), specific organic loading rate constant (K L ), microbial decay coefficient (K d ), microbial yield coefficient (Y), maximum microbial growth rate (U M ) and saturation constant (K S ) were found to be: 3.1 (g COD g VSS -1 d -1 ), 3.0 (g COD g VSS -1 d -1 ), 0.062 (d -1 ), 0.15 (g VSS g COD removed -1 ), 0.39 (d -1 ) and 2.6 (g SCOD dm -3 ), respectively.

Semi-dry thermophilic anaerobic digestion of the organic fraction of municipal solid waste: focusing on the start-up phase.

The paper concerns the results of a pilot-scale study of the simulation of the start-up phase of the thermophilic semi-dry anaerobic digestion of the organic fraction of municipal solid wastes. The aim of the study was to aid and shorten the start-up phase of the full-scale plant (500 t/d) in Verona--Ca' del Bue, where the semi-dry anaerobic digestion process is being used. The substrate used in the experimentation was the mechanically sorted organic fraction of municipal solid waste (MS-OFMSW) enriched with the putrescent fraction from the source sorted OFMSW in order to simulate the substrate which is dealt with in the Verona plant. The results of the pilot scale study agreed with literature data and previous work of the authors: it showed a specific gas production of 0.23 m3/kg TVSfeed and a gas production rate of 2.1 m3/m3 d when operating at a specific organic loading rate of 0.135 kgTVSfeed/kgTVSreacter d. No problems regarding process stability were encountered in the gradual acclimation of the biomass. The design organic loading rate of 9 kg TVSfeed/m3reactor d was reached in about 30 days, during which the total solids content in the feedwas increased. Only a partial comparison with the full scale start-up, which is now in progress, is possible: this shows an initial general concordance with the results found in previous work.

Treatment of winery wastewater by an anaerobic sequencing batch reactor

Treatment of winery wastewater was investigated using an anaerobic sequencing batch reactor (ASBR). Biogas production rate was monitored and permitted the automation of the bioreactor by a simple control system. The reactor was operated at an organic loading rate (ORL) around 8.6 gCOD/L.d with soluble chemical oxygen demand (COD) removal efficiency greater than 98%, hydraulic retention time (HRT) of 2.2 d and a specific organic loading rate (SOLR) of 0.96 gCOD/gVSS.d. The kinetics of COD and VFA removal were investigated for winery wastewater and for simple compounds such as ethanol, which is a major component of winery effluent, and acetate, which is the main volatile fatty acid (VFA) produced. The comparison of the profiles obtained with the 3 substrates shows that, overall, the acidification of the organic matter and the methanisation of the VFA follow zero order reactions, in the operating conditions of our study. The effect on the gas production rate resulted in two level periods separated by a sharp break when the acidification stage was finished and only the breaking down of the VFA continued.