Ioanna Ntaikou

Exploitation of olive oil mill wastewater for combined biohydrogen and biopolymers production

The present study aimed to the investigation of the feasibility of the combined biohydrogen and biopolymers production from OMW (Olive oil Mill Wastewater), using a two stage system. H(2) and volatile fatty acids (VFAs) were produced via anaerobic fermentation and subsequently the acidified wastewater was used as substrate for aerobic biodegradable polymer production. Two different bioreactors, one of CSTR type and a SBR were used for the anaerobic and the aerobic process respectively. The anaerobic reactor was operated at different hydraulic retention times (HRTs) with OMW, diluted 1:4 (v/v) with tap water, as feed. The main VFAs produced were acetate, butyrate and propionate, in different ratios depending on the HRT. Valerate, isovalerate and isobutyrate were also detected in small quantities. Selective effluents of the acidogenic/hydrogen producing reactor were subsequently used as feed for the aerobic reactor. The aerobic reactor was inoculated with an enriched PHAs producing bacteria culture, and was operated in sequential cycles of nitrogen offer (growth phase) and nitrogen limitation (PHAs accumulation phase). The operational program of the SBR was determined according to the results from batch test, and its performance was evaluated for a period of 100 days. During the accumulation phase butyrate was consumed preferably, indicating that the dominant PHA produced is polyhydroxybutyrate. The higher yield of PHAs observed was 8.94% (w/w) of dry biomass weight.

Olive oil mill wastewater toxicity in the marine environment: alterations of stress indices in tissues of mussel Mytilus galloprovincialis.

This study investigated the impact of olive mill wastewater (OMW) as a pollutant of the marine environment, via the detection of stress indice alterations in mussels Mytilus galloprovincialis. Due to the absence of data concerning the levels of OMW in the receiving waters, mortality test (96h) was first performed in order to estimate the range of OMW concentration where no mortality occurs. OMW concentrations ranging from 0.01 to 0.1% (v/v) showed no increased mortality and thus were used for the determination of pre-pathological alterations in tissues of mussels. In particular, mussels exposed to either 0.1 or 0.01% (v/v) OMW for 5 days showed significant alterations of stress indices in their tissues. Specifically, decreased neutral red retention (NRR) assay time values, inhibition of acetylcholinesterase (AChE) activity, as well as a significant increase of micronucleus (MN) frequency and DNA damage were detected in haemolymph/haemocytes and gills, compared with values measured in tissues of control mussels. The results of the present study showed that OMW disposal into the marine environment could induce pre-pathological alterations in marine organisms, before severe disturbances, such as disease, mortality, or population changes occur.

Valorisation of wastepaper using the fibrolytic/hydrogen producing bacterium Ruminococcus albus.

The present study aimed to investigate the biotransformation of different kinds of wastepaper to hydrogen by the fibrotylic bacterium Ruminococcus albus. Five different types i.e. paper tissue, office paper, illustrated magazine paper, paperboard and newspaper, were selected as representatives of the most common types of wastepaper found in municipal solid wastes. The percentage of total carbohydrates measured as glucose equivalents, ranged from 50% to 100% (w/w), whereas the bioconversion by R. albus ranged from 18% to 100% of their initial weigh. The only metabolic products detected in all cases were acetate, ethanol, formate, hydrogen and carbon dioxide. The hydrogen yields ranged from 46 to 280 L H(2)/kg paper, indicating that wastepaper could be a promising candidate for second generation biohydrogen production. Subsequently, hydrolysis was investigated for paper tissue and paperboard. It was shown that in both cases the degradation process could be satisfactory described by zero order kinetics and it was identified to be the rate limiting step for the whole process, controlling biomass growth and metabolites generation rate.

Production of biohydrogen from crude glycerol in an upflow column bioreactor

A continuous attached growth process for the production of biohydrogen from crude glycerol was developed. The process consisted of an anaerobic up-flow column bioreactor (UFCB), packed with cylindrical ceramic beads, which constituted the support matrix for the attachment of bacterial cells. The effect of crude glycerol concentration, pH and hydraulic retention time on glycerol conversion, hydrogen yield and metabolite distribution was investigated. It was shown that the most critical parameter for the efficient bioconversion was the pH of the influent, whereas the hydrogen yield increased with an increase in feed glycerol concentration and a decrease in the hydraulic retention time. The main soluble metabolite detected was 1,3-propanediol in all cases, followed by butyric and hexanoic acids. The latter is reported to be produced from glycerol for the first time. Acidification of the waste reached 38.5%, and the maximum H2 productivity was 107.3 ± 0.7 L/kg waste glycerol at optimal conditions.

Evaluation of a battery of marine species-based bioassays against raw and treated municipal wastewaters.

The present study evaluates a battery of marine species-based bioassays against chemically characterized municipal wastewater samples (raw and WWTP treated). We estimated Dunaliella tertiolecta growth rate inhibition (24-96h IC50 values), Artemia franciscana immobilization (24h LC50 values), mussel hemocytes viability and lipid peroxidation enhancement (in terms of neutral red retention assay/NRRT and malondialdehyde/MDA content, respectively) in influent- and WWTP effluent-treated species. We found algal growth arrest and stimulation respectively, almost similar 24hLC50 values in Artemia sp., and significantly higher adverse effects (in terms of NRRT and MDA levels) in influent-treated mussel hemocytes. Furthermore, the estimation of hatchability, yolk-sac larvae mortality (24-120hLC50) and spinal deformities (SD) in sea bream Sparus aurata showed slight variations over time, with the lowest LC50 and SD50 (representing spinal deformities at 50% of yolk-sac larvae) values to be observed in influent-treated larvae at 120h. Data interpretation (both chemical and biological) revealed that toxic endpoints, such as NRRT50, 96hIC50Dun, 120hLC50Sparus and 120hSD50Sparus, significantly related to WWTP removal efficiency and further mediated by the presence of dominant compounds, such as As and Cr, could be used for identifying main components of toxicity in wastewaters.

Biological and fermentative production of hydrogen

Abstract: This chapter discusses all the biological hydrogen production processes such as indirect and direct water biophotolysis, biological water gas shift, photo and dark fermentation and hydrogen production through microbial electrolysis cells. Dark fermentation or fermentative hydrogen production is focused on this chapter, since it is considered as the most promising compared to all biological hydrogen production methods. However, there are significant remaining barriers to practical application. The chapter includes the limitations of each process and suggests several methods that are aimed at overcoming these barriers.

Comparison of yields and properties of microbial polyhydroxyalkanoates generated from waste glycerol based substrates

The accumulation efficiency and the properties of polyhydroxyalkanoates (PHAs) produced from acidified waste glycerol (AWG) and its derivatives via an enriched microbial consortium derived from soil, were investigated in this study. AWG consisted mainly from short chain fatty acids, 1,3 propanediol and residual glycerol, which were also evaluated individually as substrates. Accumulation capacity and yields were estimated after solvent extraction and purification and PHAs were further analyzed in terms of their chemical structure, thermal properties, molecular masses and mechanical properties. The lowest accumulation capacity was noticed for non-acidified waste glycerol as carbon source which led to the generation of P(3HB), whereas for the other carbon sources co-polymers of 3HB with 3HV or 3HHx were produced. Average molecular mass weights were quite high in all cases reaching ~1.8×106Da. The thermal properties and the mechanical behavior of PHAs were shown to be highly affected by their monomeric composition, whereas it was also concluded that DSC and DMA results were in good agreement.