Enhancement of Biodegradability of Chicken Manure via the Addition of Zeolite in a Two-Stage Dry Anaerobic Digestion Configuration.

Leach bed reactors (LBRs) are dry anaerobic systems that can handle feedstocks with high solid content, like chicken manure, with minimal water addition. In this study, the chicken manure was mixed with zeolite, a novel addition, and packed in the LBR to improve biogas production. The resulting leachate was then processed in a continuous stirred tank reactor (CSTR), where most of the methane was produced. The supernatant of the CSTR was returned to the LBR. The batch mode operation of the LBR led to a varying methane production rate (MPR) with a peak in the beginning of each batch cycle when the leachate was rich in organic matter. Comparing the MPR in both systems, the peaks in the zeolite system were higher and more acute than in the control system, which was under stress, as indicated by the acetate accumulation at 2328 mg L-1. Moreover, the presence of zeolite in the LBR played a crucial role, increasing the overall methane yield from 0.142 (control experiment) to 0.171 NL CH4 per g of volatile solids of chicken manure entering the system at a solid retention time of 14 d. Zeolite also improved the stability of the system. The ammonia concentration increased gradually due to the little water entering the system and reached 3220 mg L-1 (control system) and 2730 mg L-1 (zeolite system) at the end of the experiment. It seems that zeolite favored the accumulation of the ammonia at a lower rate (14.0 mg L-1 d-1) compared to the control experiment (17.3 mg L-1 d-1). The microbial analysis of the CSTR fed on the leachate from the LBR amended with zeolite showed a higher relative abundance of Methanosaeta (83.6%) compared to the control experiment (69.1%). Both CSTRs established significantly different bacterial profiles from the inoculum after 120 days of operation (p < 0.05). Regarding the archaeal communities, there were no significant statistical differences between the CSTRs and the inoculum (p > 0.05).

Comparison of anaerobic digesters performance treating palmitic, stearic and oleic acid: determination of the LCFA kinetic constants using ADM1.

In this work, the process performance of three parallel anaerobic digesters was evaluated while treating emulsified long-chain fatty acids (LCFA) (i.e., palmitic, stearic and oleic acid) at two different organic loading rates (OLR) (2 and 4 g L-1 day-1). The digester treating palmitic acid achieved a biogas yield of 0.42 ± 0.05 L g-1 COD with a digester effluent COD of 2.3 ± 0.4 g L-1 and VFA concentrations below 250 mg L-1. Stearic acid showed lower biogas yield values (0.34 ± 0.05 L g-1 COD) with low effluent COD (2.5 ± 0.4 g L-1) and VFA concentrations (< 350 mg L-1). On the contrary, anaerobic digestion of oleic acid was accompanied with increased effluent COD (4.5 ± 0.7 g L-1) and VFA concentrations (2.7 ± 1.5 g L-1). As such, COD removal efficiency remained at 89 ± 1% compared to 95 ± 1% for the digesters treating palmitic and stearic acid. During continuous digester operation, there was a decrease in VFA concentrations (around 1-2 g L-1), combined with increasing biogas yield values up to 0.51 ± 0.04 L g-1 COD, possibly due to biomass adaptation to oleic acid. Digester foaming was recorded when the accumulated COD was higher than 200, 1200 and 500 mg COD g-1 MLSS for the digester treating palmitic, stearic and oleic acid, respectively. ADM1 simulation allowed for the determination of the maximum specific LCFA consumption rate constant (km) which was equal to 4.8, 1.6 and 8.0 day-1 for palmitic, stearic and oleic acid respectively.

Biogas Production from Sunflower Head and Stalk Residues: Effect of Alkaline Pretreatment.

Sunflower residues are considered a prominent renewable source for biogas production during anaerobic digestion (AD). However; the recalcitrant structure of this lignocellulosic substrate requires a pretreatment step for efficient biomass transformation and increased bioenergy output. The aim of the present study was to assess the effect of alkaline pretreatment of various parts of the sunflower residues (e.g., heads and stalks) on their methane yield. Experimental data showed that pretreatment at mild conditions (55 °C; 24 h; 4 g NaOH 100 g-1 total solids) caused an increase in the biochemical methane potential (BMP) of both heads and stalks of the sunflower residues as determined in batch tests. The highest methane production (268.35 ± 0.11 mL CH4 g-1 volatile solids) was achieved from the pretreated sunflower head residues. Thereafter; the effect of alkaline pretreatment of sunflower head residues was assessed in continuous mode; using continuous stirred-tank reactors (CSTRs) under two operational phases. During the first phase; the CSTRs were fed with the liquid fraction produced from the pretreatment of sunflower heads. During the second phase; the CSTRs were fed with the whole slurry resulting from the pretreatment of sunflower heads (i.e., both liquid and solid fractions). In both operating phases; it was observed that the alkaline pretreatment of the sunflower head residues had a negligible (phase I) or even a negative effect on biogas production; which was contradictory to the results of the BMP tests. It seems that; during alkaline pretreatment; this part of the sunflower residues (heads) may release inhibitory compounds; which induce a negative effect on biogas production in the long term (e.g., during continuously run digesters such as CSTR) but not in the short-term (e.g., batch tests) where the effect of the inoculum may not permit the inhibition to be established.

Assessment of the generation of empty pesticide containers in agricultural areas.

Data about the generation of empty pesticide containers (EPC) is scarce, even in countries where an EPC collection system is applied. In most cases, data refers to the total amount of EPC collected, which is lower than EPC generated depending on the extent of application of the collection project. Moreover, results are not correlated to the kind of crops, area and number of farmers involved, making impossible to use them elsewhere. This study aims at estimating EPC generation indices. It focuses on the indirect assessment of EPC generation based on information given by the agronomists of agricultural supplies stores and agricultural cooperatives (stakeholders) consulting farmers. For the study area (Pella prefecture in Greece), EPC waste production was estimated for arable crops, fruits and vegetables and it was found to range from 0.9 to 35.3 pieces/hectare depending on the crop type. The weight of empty plastic pesticide containers (EPPCweight) indices were calculated at 0.97 kg/ha and 4.36 kg/farmer/year which are close to the scarce available literature data. These results can be the basis for the design of an EPC management program in areas where data of this type of wastes is lacking. Other results of this survey indicate that stakeholders (depending on their capacity) could be motivated to organize and operate EPC collection stations as well as to help farmers to comply with the national management plan. Based on the above findings, three alternative scenarios for EPC management are proposed to provide a basis for designing an applicable regional EPC management program.

Continuous biohydrogen production from fruit wastewater at low pH conditions.

Biohydrogen production from a simulated fruit wastewater (soluble COD = 3.17 ± 0.10 g L⁻¹) was carried out in a continuous stirred tank reactor (CSTR) of 2 L operational volume without biomass inoculation, heat pre-treatment or pH adjustment, resulting in a low operational pH (3.75 ± 0.09). The hydraulic retention time (HRT) varied from 15 to 5 h. A strong negative correlation (p < 0.01) between the biogas production rate and the HRT was observed. Biogas production rates were higher at 30 °C than at 25 °C (p < 0.01), when the CSTR was operated under the same HRT. The biogas hydrogen content was estimated as high as 55.8 ± 2.3 % and 55.4 ± 2.5 % at 25 and 30 °C, respectively. The main fermentation end products were acetic and butyric acids, followed by ethanol. Significant differences (p < 0.01) during the operation of the CSTR at 25 or 30 °C were identified for butyric acid at almost all HRTs examined. Simulation of the acidogenesis process in the CSTR (based on COD and carbon balances) indicated the possible metabolic compounds produced at 25 and 30 °C reactions and provided an adequate fit of the experimental data.

Analysis of nonylphenol and nonylphenol ethoxylates in sewage sludge by high performance liquid chromatography following microwave-assisted extraction.

Nonylphenol polyethoxylates (NPnEOs) constitute a significant portion of the non-ionic surfactant market. The presence of nonylphenol (NP) in the aquatic environment is often a product of the microbial breakdown of NPEOs through discharge of industrial effluents and sewage treatment plants. The aim of this work is to develop the microwave-assisted extraction for the determination of the NP and NPEO in sewage sludge and compare this method with more traditional methods such as Soxhlet extraction and sonication. The method efficiency was evaluated as to the linearity, repeatability, accuracy, and sensitivity. Recoveries were 61.4% for NPEO and 91.4% for NP with repeatability less than 5%. The detection limit was 1.82 microg/g for NPEO and 2.86 microg/g for NP. The developed method was applied on sewage sludge samples from the sewage treatment plants of three Greek cities: Athens, Patras and Heraklion and were ranged 12.8-233.5 mg/kg for NPEO and 3.6-93 mg/kg for NP.

Fate and mobility of pharmaceuticals in solid matrices.

The sorption and mobility of six pharmaceuticals were investigated in two soil types with different organic carbon and clay content, and in bacterial biomass (aerobic and anaerobic). The pharmaceuticals examined were carbamazepine, propranolol, diclofenac sodium, clofibric acid, sulfamethoxazole and ofloxacin. The sorption experiments were performed according to the OECD test Guideline 106. The distribution coefficients determined by this batch equilibrium method varied with the pharmaceutical tested and the solid matrix type. Ofloxacin was particularly strongly adsorbed (except of the case of using anaerobic biomass for the solid matrix) while clofibric acid was found to be weakly adsorbed. The fate of pharmaceuticals in soil was also assessed using lysimeters. Important parameters that were studied were: the pharmaceutical loading rate and the hydraulic loading rate for adsorption and the rate and duration of a "rain" event for desorption. Major differences in the mobility of the six pharmaceuticals were observed and correlated with the adsorption/desorption properties of the compounds.

Exploitation of olive mill wastewater and liquid cow manure for biogas production.

Co-digestion of organic waste streams is an innovative technology for the reduction of methane/greenhouse gas emissions. Different organic substrates are combined to generate a homogeneous mixture as input to the anaerobic reactor in order to increase process performance, realize a more efficient use of equipment and cost-sharing by processing multiple waste streams in a single facility. In this study, the potential of anaerobic digestion for the treatment of a mixture containing olive mill wastewater (OMW) and liquid cow manure (LCM) using a two-stage process has been evaluated by using two continuously stirred tank reactors (CSTRs) under mesophilic conditions (35 degrees C) in order to separately monitor and control the processes of acidogenesis and methanogenesis. The overall process was studied with a hydraulic retention time (HRT) of 19 days. The digester was continuously fed with an influent composed (v/v) of 20% OMW and 80% LCM. The average removal of dissolved and total COD was 63.2% and 50%, respectively. The volatile solids (VS) removal was 34.2% for the examined mixture of feedstocks operating the system at an overall OLR of 3.63 g CODL(reactor)(-1)d(-1). Methane production rate at the steady state reached 0.91 L CH(4)L(reactor)(-1)d(-1) or 250.9L CH(4) at standard temperature and pressure conditions (STP) per kg COD fed to the system.

On the fate of LAS, NPEOs and DEHP in municipal sewage sludge during composting.

The fate of hydrophobic xenobiotic pollutants such as linear alkylbenzene sulfonates (LAS), nonylphenol ethoxylates (NPEO) and di-ethyl-hexyl phthalate (DEHP) during sewage sludge composting was addressed in this work. The experiments were conducted in a fully automated in-vessel autothermal composting system which was fed with a mixture of primary and secondary sludge and manure. The mixture composition was determined to achieve satisfactory humidity, C/N ratio and free air space (FAS). The effect of various parameters, such as the initial xenobiotic concentration, the presence of multiple xenobiotic compounds and the temperature of composting material sustained during the process on the xenobiotics biodegradation kinetics was investigated. It was generally established that significant xenobiotic reduction is achievable through composting under all conditions tested. According to the obtained results, the presence of LAS, NPEO and DEHP even at higher concentrations was not inhibitory to the bioprocess. However, the presence of multiple xenobiotic compounds such as NPEO, NP and DEHP in the sludge can influence LAS removal during LAS composting.

Using cheese whey for hydrogen and methane generation in a two-stage continuous process with alternative pH controlling approaches.

This study focuses on the exploitation of cheese whey as a source for hydrogen and methane, in a two-stage continuous process. Mesophilic fermentative hydrogen production from undiluted cheese whey was investigated at a hydraulic retention time (HRT) of 24 h. Alkalinity addition (NaHCO(3)) or an automatic pH controller were used, to maintain the pH culture at a constant value of 5.2. The hydrogen production rate was 2.9+/-0.2 L/Lreactor/d, while the yield of hydrogen produced was approximately 0.78+/-0.05 mol H(2)/mol glucose consumed, with alkalinity addition, while the respective values when using pH control were 1.9+/-0.1 L/Lreactor/d and 0.61+/-0.04 mol H(2)/mol glucose consumed. The corresponding yields of hydrogen produced were 2.9 L of H(2)/L cheese whey and 1.9 L of H(2)/L cheese whey, respectively. The effluent from the hydrogenogenic reactor was further digested to biogas in a continuous mesophilic anaerobic bioreactor. The anaerobic digester was operated at an HRT of 20 d and produced approximately 1L CH(4)/d, corresponding to a yield of 6.7 L CH(4)/L of influent. The chemical oxygen demand (COD) elimination reached 95.3% demonstrating that cheese whey could be efficiently used for hydrogen and methane production, in a two-stage process.

Hydrogen and methane production through two-stage mesophilic anaerobic digestion of olive pulp.

The present study focused on the anaerobic biohydrogen production from olive pulp (two phase olive mill wastes, TPOMW) and the subsequent anaerobic treatment of the effluent for methane production under mesophilic conditions in a two-stage process. Biohydrogen production from water-diluted (1:4) olive pulp was investigated at hydraulic retention times (HRT) of 30 h, 14.5 h and 7.5 h while methane production from the effluent of hydrogenogenic reactor was studied at 20 d, 15 d, 10d and 5d HRT. In comparison with previous studies, it has been shown that the thermophilic hydrogen production process was more efficient than the mesophilic one in both hydrogen production rate and yield. The methanogenic reactor was successfully operated at 20, 15 and 10 days HRT while it failed when an HRT of 5 days was applied. Methane productivity reached the maximum value of 1.13+/-0.08 L/L/d at 10 days HRT whereas the methane yield increased with the HRT. The Anaerobic Digestion Model no. 1 (ADM1) was applied to the obtained experimental data from the methanogenic reactor to simulate the digester response at all HRT tested. The ability of the model to predict the experimental results was evident even in the case of the process failure, thus implying that the ADM1 could be a valuable tool for process design even in the case of a complex feedstock. In general, the two-stage anaerobic digestion proved to be a stable, reliable and effective process for energy recovery and stabilization treatment of olive pulp.

Monitoring and control of anaerobic reactors.

The current status in monitoring and control of anaerobic reactors is reviewed. The influence of reactor design and waste composition on the possible monitoring and control schemes is examined. After defining the overall control structure, and possible control objectives, the possible process measurements are reviewed in detail. In the sequel, possible manipulated variables, such as the hydraulic retention time, the organic loading rate, the sludge retention time, temperature, pH and alkalinity are evaluated with respect to the two main reactor types: high-rate and low-rate. Finally, the different control approaches that have been used are comprehensively described. These include simple and adaptive controllers, as well as more recent developments such as fuzzy controllers, knowledge-based controllers and controllers based on neural networks.