Evaluating the biogas potential of the dry fraction from pretreatment of food waste from households.

At the waste handling company NSR, Helsingborg, Sweden, the food waste fraction of source separated municipal solid waste is pretreated to obtain a liquid fraction, which is used for biogas production, and a dry fraction, which is at present incinerated. This pretreatment and separation is performed to remove impurities, however also some of the organic material is removed. The possibility of realising the methane potential of the dry fraction through batch-wise dry anaerobic digestion was investigated. The anaerobic digestion technique used was a two-stage process consisting of a static leach bed reactor and a methane reactor. Treatment of the dry fraction alone and in a mixture with structural material was tested to investigate the effect on the porosity of the leach bed. A tracer experiment was carried out to investigate the liquid flow through the leach beds, and this method proved useful in demonstrating a more homogenous flow through the leach bed when structural material was added. Addition of structural material to the dry fraction was needed to achieve a functional digestion process. A methane yield of 98 m3/ton was obtained from the dry fraction mixed with structural material after 76 days of digestion. This was in the same range as obtained in the laboratory scale biochemical methane potential test, showing that it was possible to extract the organic content in the dry fraction in this type of dry digestion system for the production of methane.

Biogas production from wheat straw in batch and UASB reactors: the roles of pretreatment and seaweed hydrolysate as a co-substrate.

This research evaluated biogas production in batch and UASB reactors from pilot-scale acid catalysed steam pretreated and enzymatic hydrolysed wheat straw. The results showed that the pretreatment was efficient and, a sugar yield of 95% was obtained. The pretreatment improved the methane yield (0.28 m(3)/kg VS(added)) by 57% compared to untreated straw. Treatment of the straw hydrolysate with nutrient supplementation in a UASB reactor resulted in a high methane production rate, 2.70 m(3)/m(3).d at a sustainable OLR of 10.4 kg COD/m(3).d and with a COD reduction of 94%. Alternatively, co-digestion of the straw and seaweed hydrolysates in a UASB reactor also maintained a stable anaerobic process and can thus reduce the cost of nutrients addition. We have shown that biogas production from wheat straw can be competitive by pretreatment, high methane production rate in UASB reactors and also by co-digestion with seaweed hydrolysate.

Evaluation of biogas production from seaweed in batch tests and in UASB reactors combined with the removal of heavy metals.

Seaweed can be anaerobically digested for the production of energy-rich methane. However, the use of seaweed digestate as a fertilizer may be restricted because of the high heavy metal content especially cadmium. Reducing the concentration of heavy metals in the digestate will enable its use as a fertilizer. In this laboratory-scale study, the potential of seaweed and its leachate in the production of methane were evaluated in batch tests. The effect of removing the heavy metals from seaweed leachate was evaluated in both batch test and treatment in an upflow anaerobic sludge blanket (UASB) reactor. The heavy metals were removed from seaweed leachate using an imminodiacetic acid (IDA) polyacrylamide cryogel carrier. The methane yield obtained in the anaerobic digestion of seaweed was 0.12 N l CH(4)/g VS(added). The same methane yield was obtained when the seaweed leachate was used for methane production. The IDA-cryogel carrier was efficient in removing Cd(2+), Cu(2+), Ni(2+) and Zn(2+) ions from seaweed leachate. The removal of heavy metals in the seaweed leachate led to a decrease in the methane yield. The maximum sustainable organic loading rate (OLR) attained in the UASB reactor was 20.6 g tCOD/l/day corresponding to a hydraulic retention time (HRT) of 12 h and with a total COD removal efficiency of about 81%. Hydrolysis and treatment with IDA cryogel reduced the heavy metals content in the seaweed leachate before methane production. This study also demonstrated the suitability of the treatment of seaweed leachate in a UASB reactor.

An update and optimisation of oligonucleotide probes targeting methanogenic Archaea for use in fluorescence in situ hybridisation (FISH).

Fluorescence in situ hybridisation (FISH) is a common and popular method used to investigate microbial populations in natural and engineered environments. DNA oligonucleotide probes require accurate determination of the optimal experimental conditions for their use in FISH. Oligonucleotides targeting the rRNA of methanogenic Archaea at various taxonomic levels have previously been published, although when applied in FISH, no optimisation data has been presented. In this study, 3000 Euryarchaeota 16S rRNA gene sequences were phylogenetically analysed and previously published oligonucleotides were evaluated for target group accuracy. Where necessary, modifications were introduced or new probes were designed. The updated set of probes was optimised for use in FISH for a more accurate detection of methanogenic Archaea.

Biodegradation of nonylphenol in a continuous bioreactor at low temperatures and effects on the microbial population.

A packed-bed bioreactor inoculated with a mixed culture obtained from a contaminated site was used to continuously treat a saturated solution of nonylphenol. The reactor was operated at feeding rates of 13-112 ml h-1 and temperatures of 5.5, 10, and 15 degrees C. Optimal bioreactor performance was achieved at 10 degrees C and at a feeding rate of 84 ml h-1 (with a removal rate of 43 mg l-1 day-1 of nonylphenol). No endocrine activity was observed in the effluent of the bioreactor at any of the temperatures tested, and the only metabolic products found were branched carboxylic acids and alkanes (lacking an aromatic ring). The study of the microbial populations in the biofilm at the three temperatures tested using fluorescence in situ hybridization showed that all the bacterial species that could be identified belonged to the phylum Proteobacteria. The most abundant class identified at all three temperatures was beta-Proteobacteria. The proportions of bacteria that bound to the specific probes among the total population, identified with the bacterial probe EUB338MIX, were 60, 43, and 24% at 15, 10, and 5.5 degrees C, respectively.