Denitrifying anaerobic methane oxidation (DAMO) cultures: Factors affecting their enrichment, performance and integration with anammox bacteria.

The recently discovered process, denitrifying anaerobic methane oxidation (DAMO), links the carbon and nitrogen biogeochemical cycles via coupling the anaerobic oxidation of methane to denitrification. The DAMO process, in this respect, has the potential to mitigate the greenhouse effect through the assimilation of dissolved methane. Denitrification via methane oxidation rather than organic matter, provides a new perspective to performing this once thought to be well established process. The two main species responsible for this process are "Candidatus Methylomirabilis oxyfera (M. oxyfera), and "Candidatus Methanoperedens nitroreducens" (M. nitroreducens). M. oxyfera is responsible of reducing nitrite while M. nitroreducens reduces nitrate to nitrite. These two microorganisms, despite their different pathways, were found to exist together in nature through a syntrophic relationship. Their co-existence with anaerobic ammonium oxidation (Anammox) bacteria was also revealed in the last decade. Anammox bacteria are chemolithoautotrophs, converting ammonium and nitrite to N2 and nitrate. They are responsible for the release of more than 50% of oceanic N2, hence play an important role in the global nitrogen cycle. Factors leading to the enrichment of DAMO cultures and their cultivation with Anammox cultures are of significance for improved nitrogen removal systems with decreased greenhouse effect, and even for further full-scale applications. This study, therefore, aims to present an updated review of the DAMO process, by focusing on the factors that might have a significant role in enrichment of DAMO microorganisms and their co-existence with Anammox bacteria. Factors such as temperature, pH, inoculum and feed type, trace metals and reactor configuration are among the ones discussed in detail. Factors, which have not been investigated, are also elucidated to provide a better understanding of the process and set research goals that will aid in the development of DAMO-centered wastewater treatment alternatives.

High-rate anaerobic treatment of digestate using fixed film reactors.

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57-62% in 1.3-1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395-0.430 Lbiogas/g VSadded which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36-47%) and greenhouse gas capture (over 14.5-18.1 tCO2e/d per m3 digestate) were also recorded in the anaerobic fixed-film reactors.

Wastewater disposal to landfill-sites: a synergistic solution for centralized management of olive mill wastewater and enhanced production of landfill gas.

The present paper focuses on a largely unexplored field of landfill-site valorization in combination with the construction and operation of a centralized olive mill wastewater (OMW) treatment facility. The latter consists of a wastewater storage lagoon, a compact anaerobic digester operated all year round and a landfill-based final disposal system. Key elements for process design, such as wastewater pre-treatment, application method and rate, and the potential effects on leachate quantity and quality, are discussed based on a comprehensive literature review. Furthermore, a case-study for eight (8) olive mill enterprises generating 8700 m(3) of wastewater per year, was conceptually designed in order to calculate the capital and operational costs of the facility (transportation, storage, treatment, final disposal). The proposed facility was found to be economically self-sufficient, as long as the transportation costs of the OMW were maintained at ≤4.0 €/m(3). Despite that EU Landfill Directive prohibits wastewater disposal to landfills, controlled application, based on appropriately designed pre-treatment system and specific loading rates, may provide improved landfill stabilization and a sustainable (environmentally and economically) solution for effluents generated by numerous small- and medium-size olive mill enterprises dispersed in the Mediterranean region.

Investigation of the effect of culture type on biological hydrogen production from sugar industry wastes.

The bio-hydrogen generation potential of sugar industry wastes was investigated. In the first part of the study, acidogenic anaerobic culture was enriched from the mixed anaerobic culture (MAC) through acidification of glucose. In the second part of the study, glucose acclimated acidogenic seed was used, along with the indigenous microorganisms, MAC, 2-bromoethanesulfonate treated MAC and heat treated MAC. Two different COD levels (4.5 and 30g/L COD) were investigated for each culture type. Reactors with initial COD concentration of 4.5g/L had higher H(2) yields (20.3-87.7mL H(2)/g COD) than the reactors with initial COD concentration of 30g/L (0.9-16.6mL H(2)/g COD). The 2-bromoethanesulfonate and heat treatment of MAC inhibited the methanogenic activity, but did not increase the H(2) production yield. The maximum H(2) production (87.7mL H(2)/g COD) and minimum methanogenic activity were observed in the unseeded reactor with 4.5g/L of initial COD.

Environmental factors shaping the ecological niches of ammonia-oxidizing archaea.

For more than 100 years it was believed that bacteria were the only group responsible for the oxidation of ammonia. However, recently, a new strain of archaea bearing a putative ammonia monooxygenase subunit A (amoA) gene and able to oxidize ammonia was isolated from a marine aquarium tank. Ammonia-oxidizing archaea (AOA) were subsequently discovered in many ecosystems of varied characteristics and even found as the predominant causal organisms in some environments. Here, we summarize the current knowledge on the environmental conditions related to the presence of AOA and discuss the possible site-related properties. Considering these data, we deduct the possible niches of AOA based on pH, sulfide and phosphate levels. It is proposed that the AOA might be important actors within the nitrogen cycle in low-nutrient, low-pH, and sulfide-containing environments.

Partial nitrification achieved by pulse sulfide doses in a sequential batch reactor.

A nitrifying sequential batch reactor operated under 2-day cyclic aerobic and anoxic conditions was pulse dosed with incremental sulfide concentrations during anoxic conditions. The nitrite-oxidizing bacteria were found to be more sensitive to sulfide than the ammonia oxidizers. A maximum of nitrite-N to (nitrite-N + nitrate-N) accumulation ratio of 0.75 was obtained at an initial pulse sulfide-S concentration of 45 mg/L under pH control at 7.5 +/- 0.2 and fully mixing conditions. Total ammonium nitrogen was removed almost 100% at a removal rate of 0.73 +/- 0.05 g/L x day, achieved during the aerobic days of the cycles. Denaturing gradientgel electrophoresis (DGGE) and fluorescence in situ hybridization (FISH) analyses indicated the shift in the ammonia- and nitrite-oxidizing populations triggered by sulfide addition, partial nitrification, and subsequent recovery to complete nitrification. Interestingly, archaeal amoA genes were retrieved under the conditions of sulfide addition. These results indicate that the pulse sulfide application can be used as a tool to accumulate nitrite, which is of importance for the subsequent anaerobic ammonium oxidation (anammox) process in the achievement of complete nitrogen removal.

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors.

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88-92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44-86% and 86-94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/lday (76 microg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.