Possibilities for energy recovery from sludge at Chişinȃu wastewater treatment plant have been investigated and evaluated. One way of recovering energy from sludge is to produce biogas through anaerobic digestion. Which method of biogas usage that is to prefer in Chişinȃu has been evaluated from a cost-efficiency point of view. There is a possibility that a new waste incineration plant will be built next to the wastewater treatment plant, and therefore solutions that benefit from a co-operation have been discussed. The results show that biogas production would be suitable and profitable in a long time perspective if the gas is used for combined heat and power production. Though, the rather high, economical interest rates in Moldova are an obstacle for profitability.

Two species of emergent macrophytes, Typha latifolia (common cattail) and Phalaris arundinacea (reed canary grass) were evaluated as substrates for biogas production. The specific methane yield for each plant was obtained by batch wise anaerobic digestion in 300-mL bottles. Three different pretreatments were evaluated for increased biogas production; mechanical milling, alkaline treatment with lime and fungal degradation with Pleurotus ostreatus (oyseter mushroom).The methane yield for Typha latifolia and Phalaris arundinacea was determined to 300 and 323mL methane per g VS, respectively. There was no statistical difference in methane yield between the two species. Milling pretreatment increased the biogas yield with 16 % by average compared to untreated plant. Alkaline pretreatment with lime increased the biogas yield with 27 % at roomtemp. and 22 % at 55 °C. The fungal pretreatment decreased the biogas production by 20 % and is probably not suitable for this kind of substrate.The results showed that emergent macrophytes have a biogas yield similar to other plants already tested (grasses) and commonly used (pasture crops) in large scale reactors. However, emergent macrophytes and grasses cause mechanical problems in a reactor due to their structure. Probably some kind of milling must be done to decrease the fiber length of the emergent macrophytes. The costs for harvest, transport, handling and possible pretreatment of the emergent macrophytes have to be estimated and included in the overall cost calculations. This can tell if emergent macrophytes should be used as a substrate for biogas production.

The production of biogas via anaerobic digestion is an effective technology for converting organic waste into renewable fuel. Using the Technological Innovation System (TIS) theory for assessing emerging technologies a comparison between the British and Swedish biogas sectors is carried out. There are seven components to a TIS allowing the sector to be broken down, a potential scheme for the connection of the functions is illustrated. The Swedish biogas sector is at a more advanced stage of development due to long-term governmental support both financially and through stringent environmental laws. Overall the Swedish government has been an effective system builder allowing the Swedish biogas sector to expand. The British biogas sector is conversely less advanced due to lack of this long-term support, although the scene is beginning to change as the government positions itself as a more effective system builder. Several lessons can be learnt from the Swedish biogas sector; longterm financial support for renewable energy is required and stringent organic waste disposal laws both encourage the development of biogas.

Biogas, a mixture of methane and carbon dioxide, is produced in the anaerobic digestion of sewage sludge. After anaerobic digestion, the digested sludge is often allowed to degas for one or two days. This gas is seldom utilised, but if the degassing could be accelerated, utilisation would be easier. Ultrasound can be used as a pretreatment method for waste activated sludge. It has a disintegrating effect on the sludge and causes lysis of bacteria in the sludge. It also speeds up the hydrolysis; the limiting step of anaerobic digestion of waste activated sludge. Ultrasound can be used to degas waterbased liquids. Ultrasonic degassing of sewage sludge has not been examined previously. The present study aims to investigate the effect of ultrasound on waste activated sludge as well as the potential of ultrasound to speed up the degassing of digested sludge. A semi-continuous, lab-scale digestion experiment was performed with four reactors: two receiving untreated sludge and two receiving treated sludge. The effect of the sonicator was 420 W and the treatment time was 6 min, which corresponds to an energy input of 8.4 kWh/m3. Total solids (TS) of the waste activated sludge was ~3.5 %. The ultrasonic treatment caused an increase in gas production of 13 %. There was no difference in methane content. The concentration of filterable chemical oxygen demand (fCOD) increased 375 %, or from 2.8 % to 11 % of total COD. In terms of energy loss/gain the increase in gas production resulted in a loss of 2.7 kWh/m3, i.e. more energy is needed to treat the sludge than the potential energy of the increased gas production. However, if the sludge is thickened to a TS >5 %, a net energy gain should be reached. The effect of ultrasound on the degassing of digested sludge was examined in three barrels. The degassing was measured with and without circulation as well as with ultrasonic treatment. The digested sludge had a gas emission rate of 115 L/(m3 day). No direct burst of gas occurred due to ultrasonic treatment. Over two days more gas was emitted from the barrel equipped with ultrasound, probably due to an induced post-digestion. Thus, ultrasonic pretreatment of waste activated sludge increases the biogas yield. It is inconclusive, whether ultrasonic treatment of digested sludge effects the degassing or not.

Constructed wetlands are largely used for water treatment both in agricultural land and for treating water from municipal and industrial waste. These wetlands need to be managed in order to work properly. How to deal with the large amount of vegetation harvested in the wetlands has withdrawn a great concern. The application of using wetland biomass as the co-substrates in anaerobic digestion was studied in this project. Plant materials, mostly Phragmites australis (common reed) from three different wetlands were used as raw material to produce biogas. The methane production using reed material harvested from municipal wastewater, industrial wastewater and an agricultural wetland are 66, 106, 144 ml/g VS respectively, which were lower than the suggested number 180ml/g VS. The gas potential remains a lot to be improved such as harvesting at summer to reduce the lignin content and changing the co-digestion mixing level to adjust to the optimal C/N ratio. Chemical analyses were performed concerning the gas yield and the residue quality. The digested residues showed a low concentration of cadmium, providing a non-toxic possibility to be spread on farm land as fertilizers, and closing the nutrient circle from land into water and back to land again. Pretreatments in the biogas process are usually focusing on the reduction of the lignocellulosic content in the raw material. Assessment of costs and benefits is needed for using wetland reed in the biogas production and applying any pretreatment methods.

Anaerobic digestion (AD) is an effective way to convert animal manures into profitable byproducts as well as to reduce the pollution of water, air, and soil caused by these wastes. Conventional high-rate anaerobic reactors cannot effectively process high-solids containing animal manures. The two-phase configuration for AD has several advantages over conventional one-phase processes such as increased stability of the process, smaller and cost efficient process configurations, etc. This study investigated the two-phase AD of dairy manure with particular emphasis on the effects of solids retention time (SRT), organic loading rate (OLR) and pH on anaerobic acidification of unscreened dairy manure / the effects of temperature on biogas production and the comparison of one-phase and two-phase system performance of AD. The results revealed that pre-acidification of dairy manure in daily-fed continuously-mixed reactors with no recycle led to substantial volatile fatty acids production. The optimum operational conditions for anaerobic acidification were determined as SRT and OLR of 2 days and 15 g VS/L.day. The pH control at a range of 5.0-5.5 was not found to be necessary for optimum acidification. Molecular analysis indicated that acidogenic bacteria population increased whilst the aerobic bacteria population decreased as time passed in acidogenic phase. The effect of temperature was clearly observed on biogas production efficiency. Two-phase configuration was determined more efficient than one-phase system. The biogas production in two-phase system was calculated to be 41% higher than that of the one-phase for the same OLR of 3.5 g VS/L.day. This translates into significant performance improvement and reduced volume requirement. This finding represents a further step in the achievement of wider use of simple anaerobic reactor configurations in rural areas.

The main objective of this study was to investigate two of the possible exploitation routes of anaerobic digestion (acid-phase and methane-phase) for the treatment of sugar-beet processing wastes, while producing valuable biobased products. For this purpose, four sets of laboratory experiments were carried out in a stepwise fashion: First, in the biochemical methane potential (BMP) assay (Set-up 1) wastewater and beet-pulp were efficiently digested (63.7&ndash / 87.3% COD removal and 69.6&ndash / 89.3% VS reduction) in batch anaerobic reactors. Secondly, wastewater and beet-pulp could simultaneously be converted to VFAs in acidogenic anaerobic reactors with considerable acidification degrees (43.8&ndash / 52.9%), optimizing the operational conditions (Set-up 2). Then, the produced VFAs were recovered by liquid-liquid extraction (Set-up 3), in which highest VFA recoveries (60.7&ndash / 97.6%) were observed at 20% trioctylphosphine oxide (TOPO) in kerosene with KD values ranging between 1.54 and 40.79 at pH 2.5. Finally, methane-phase anaerobic digestion was evaluated in two different reactor configurations, namely fed-batch continuously mixed reactor (FCMR) and anaerobic sequencing batch reactor (ASBR) (Set-up 4). Methane production yield of 255 &plusmn / 11 mL/g COD-added was increased to 337 &plusmn / 15 mL/g COD-added (32.2% increase in methane yield) when configuration was changed from FCMR to ASBR. In addition, tCOD removal was increased from 68.7 &plusmn / 2.2 to 79.7 &plusmn / 1.1%. Based on the result obtained in this study, it is postulated that, biorefining of sugar-beet processing wastes by anaerobic digestion can not only be a solution for environmental related problems, but also contribute to resource conservation and sustainable production via valuable bio-based product formation.

Xenobiotic compounds, which are exclusively man made, are produced in large quantities every year and released to the environment. Besides, anaerobic sludge digestion offers advantage in co-treatment of hazardous substances produced by the industry. The performance of the digesters can be monitored by modeling efforts. In this study, Anaerobic Digestion Model No.1 (ADM1) was calibrated, and validated for full-scale digester, lab-scale digester, and lab-scale digester seeded with totally different anaerobic biomass than that of full-scale digester. The model xenobiotic compound, a mono azo dye RO107, was co-treated with sewage sludge in an anaerobic digester. High removal efficiencies as 98% was found for azo dye at standard operating conditions of anaerobic digesters. The digester performance was not effected from azo dye or its reduction products. The dye reduction mechanism was modeled by biochemical mechanism due to unspecific enzymes and by chemical mechanism due to sulfide reduction. Some of the dye metabolites were suggested to be degraded by aerobic biotreatment. The anaerobic reduction metabolites of RO107 were identified as 2-(4-aminophenylsulfonyl) ethanol and 2,5-diamino-4-formamidobenzenesulfonic acid, and sulfanilic acid.

The main objective of this study was to investigate the removal and recovery of nutrients from anaerobic digestion residues of poultry manure through struvite (MgNH4PO4.6H2O, MAP) precipitation. To this purpose, three sets of laboratory experiments were conducted. In the first set, separate and co-digestion of poultry manure and sewage sludge were studied in laboratory-scale mesophilic anaerobic batch reactors and subsequent struvite precipitation experiments were conducted with the reactors effluents. The effects of important parameters on struvite precipitation were investigated and it is illustrated that up to 89 % of NH4-N, 84 % PO4-P and 42 % COD removals were possible. In the second set, the effluents of a full-scale co-digestion plant utilizing poultry manure and maize silage were subjected to struvite precipitation experiments. Acidic phosphorus-dissolution process was successfully applied to the solid phase effluents to obtain phosphorus-enriched solution. By the addition of external Mg and P more than 90% of NH4-N and PO4-P were recovered from phosphorus-enriched solution, whereas the addition of only Mg led to partial recovery of NH4-N. In the third set, the effluents of a full-scale poultry manure digester were subjected to struvite precipitation experiments. The findings illustrated that Ca has inhibitory effects on the struvite reaction and lead to formation of hydroxlyapatite and amorphous calcium phosphates together with struvite. Based on the results obtained in this study, it is postulated that, struvite precipitation is a viable option for the recovery of the nutrients in the anaerobically digested poultry manure. This study illustrated that, poultry manure, if managed properly, could meet one-fourth of Turkey&amp / #8217 / s domestic fertilizer demand.

In this study, bio-hydrogen generation potential of sugar-beet processing wastes (sugar-beet processing wastewater and beet-pulp) through dark fermentation was investigated. For this purpose, four different experimental set-ups were used. In the first set-up, sugar-beet processing wastewater was used along with four different cultures to investigate the effect of culture type on bio-hydrogen production. In addition, unseeded reactor was prepared to investigate bio-hydrogen production potential of indigenous microorganisms. The highest bio-hydrogen production yield (87.7 mL H2/g COD) was observed in the unseeded reactor. In the second set-up, beet-pulp was compared with sugar-beet processing wastewater in terms of bio-hydrogen generation potentials at an initial COD level of 4.5 g/L. In the third set-up, bio-hydrogen productivities of only beet-pulp and co-digestion of beet-pulp and sugar-beet processing wastewater at high COD values were investigated. The results of third set-up revealed that the reactor fed by 20 g/L COD beet-pulp provided the highest bio-hydrogen production yield (95.6 mL H2 /g COD). Finally, in the fourth set-up, the effects of five different pretreatment methods on solubilization of beet-pulp were investigated. Then, three out of five pretreatment methods were chosen to compare the corresponding bio-hydrogen productivities. Maximum bio-hydrogen production yield (115.6 mL H2/g COD) was observed in reactor which contained alkaline pretreated beet-pulp. Based on the results obtained in this study, it is postulated that, bio-hydrogen production from sugar-beet processing wastes by dark fermentation can not only enable waste minimization but also contribute to sustainability via valuable bio-based product formation from wastes, namely bio-hydrogen.