Anaerobic protozoa and their growth in biomethanation systems.

This study was to investigate growth of protozoa and its influence on biodegradation in anaerobic treatment systems. It was done by specifically controlling and monitoring growth of protozoa versus degradation in continuous stirred anaerobic reactors and batch anaerobic reactors. Occurrence of a diverse protozoa population such as the ciliates, Prorodon, Vorticella, Cyclidium, Spathidium, Loxodes, Metopus were observed in stable anaerobic systems and the flagellates, Rhynchomonas, Naeglaria, Amoeboflagellates, Tetramitus, Trepomonas and Bodo during increased VFA concentration and affected periods of biomethanation. The abundance of ciliates in the anaerobic system had significant correlation with the reduction of MLSS, increased rate of COD removal and higher methane production. The results of this study thus tend to relate increased anaerobic degradation with the abundance of protozoa, mainly ciliates, which indicate their possible involvement in the process. Present study also reveals that performance of anaerobic process can be assessed by monitoring the protozoa population in the system.

Involvement of protozoa in anaerobic wastewater treatment process.

It is only very rarely recognised in literature that anaerobic reactors may contain protozoa in addition to various bacterial and archeal groups. The role of protozoa in anaerobic degradation was studied in anaerobic continuous stirred tank reactors (CSTR) and batch tests. Anaerobic protozoa, especially the ciliated protozoa, have direct influence on the performance of CSTR at all organic loading rates (1-2g CODl(-1)d(-1)) and retention times (5-10 days). The studies revealed that chemical oxygen demand (COD) removal is strongly correlated to ciliate density in CSTR fed with oleate (suspended COD) and acetate (soluble COD). There was no significant difference in COD removal between reactors fed suspended COD and those fed soluble COD. However, the diversity and number of ciliates is greater in CSTR fed with particulate feed. The mixed liquor suspended solids (MLSS) representing biomass was significantly lower (16-34%) in CSTR with protozoa. In batch tests, increased COD removal and methane production was observed in sludge having ciliates as compared with sludge without protozoa. Methane production increased linearly with number of ciliates (R(2)=0.96) in batch tests with protozoa. Direct utilization of COD by flagellates and ciliates was observed in bacteria-suppressed cultures. The technological importance of these results is that reactors with protozoa-rich sludge can enhance the rate of mineralization of complex wastewater, especially wastewater containing particulate COD.

Isolation and culturing of a most common anaerobic ciliate, Metopus sp.

The study includes isolation of anaerobic ciliate, Metopus sp. from an anaerobic reactor and development of its monoculture under laboratory conditions. Separation by centrifugation followed by micromanipulatory isolation resulted in obtaining pure Metopus culture with less bacterial contamination. The isolated Metopus sp. had the mean dimensions of 32 x 123 microm with the generation time of 53 h. Among the different basal media tried, the ciliate mineral medium (CMV) with 1% wheat powder suspension was the most suitable one for Metopus growth. The temperature and pH ranges, for the best growth of Metopus, were 30-35 degrees C and 6-7, respectively. Higher concentrations of volatile fatty acids (VFA) such as acetate, butyrate and propionate had adverse effect on Metopus growth and prevented its growth beyond 0.05 M concentration. Maximum COD removal was in CMV medium by the growth of anaerobic Metopus sp.

The Buoyant Filter Bioreactor: a high-rate anaerobic reactor for complex wastewater--process dynamics with dairy effluent.

A novel high-rate anaerobic reactor, called "Buoyant Filter Bioreactor" (BFBR), has been developed for treating lipid-rich complex wastewater. The BFBR is able to decouple the biomass and insoluble COD retention time from the hydraulic retention time by means of a granular filter bed made of buoyant polystyrene beads. Filter clogging is prevented by an automatic backwash driven by biogas release, which fluidizes the granular filter bed in a downward direction. During filter backwash, the solids captured in the filter are reintroduced into the reaction zone of the reactor. The reaction zone is provided with a mixing system, which is independent of the hydraulic retention time. The performance of a laboratory-scale BFBR was studied for the treatment of dairy effluent, chosen as a model complex wastewater. The dairy effluent was not pre-treated for fat removal. The BFBR was operated over 400 d and showed greater than 85% COD removal at 10 kg COD/(m3/d). The COD conversion to methane in the BFBR was essentially complete. The BFBR performance improved with age, and with feed containing 3200 mg COD/l, the treated effluent had 120 mg COD/l and no turbidity. The hold-up of degradable biosolids, including scum, inside the BFBR was estimated using starvation tests. When load is increased, scum accumulates inside the BFBR and then decays after undergoing change from hydrophobic to hydrophilic. This is explained as the accumulation of fat solids, its conversion to insoluble long chain fatty acids and its further solubilization and degradation.

Treatment of sulphide containing wastewater with sulphur recovery in a novel reverse fluidized loop reactor (RFLR).

A novel aerobic bioreactor, the reverse fluidized loop reactor (RFLR) was tested for recovering sulphur from aqueous sulphide in this study. The RFLR contained buoyant carrier particles on which chemolithotrophic sulphide oxidizing bacteria formed a biofilm, which oxidized sulphide to sulphur and separated from the aqueous phase. The redox potential of the RFLR was regulated to control the oxygenation of sulphide for sulphur production. The RFLR was operated without any pH control and under various controlled pHs. The sulphide removal and nature of products formed under various sulphide loading rates and pH were examined. Under pH uncontrolled state, 95% of sulphur was recovered up to 11 kg sulphide/m3 d. The maximum sulphide loading supplied to the reactor was 30 kg sulphide/m3 d at pH 8, of which 90% was completely oxidized and 65% recovered as sulphur. The decline in bacterial sulphide oxidation leads to chemical oxidation of sulphide and subsequent accumulation of intermediary products such as thiosulphate and polysulphide in the reactor.

Relationship between Cell Surface Properties and Transport of Bacteria through Soil.

A study was conducted to relate the properties of Enterobacter, Pseudomonas, Bacillus, Achromobacter, Flavobacterium, and Arthrobacter strains to their transport with water moving through soil. The bacteria differed markedly in their extent of transport; their hydrophobicity, as measured by adherence to n-octane and by hydrophobic-interaction chromatography; and their net surface electrostatic charge, as determined by electrostatic interaction chromatography and by measurements of the zeta potential. Transport of the 19 strains through Kendaia loam or their retention by this soil was not correlated with hydrophobicities or net surface charges of the cells or the presence of capsules. Among 10 strains tested, the presence of flagella was also not correlated with transport. Retention was statistically related to cell size, with bacteria shorter than 1.0 mum usually showing higher percentages of cells being transported through the soil. We suggest that more than one characteristic of bacterial cells determines whether the organisms are transported through soil with moving water.

Factors affecting the microbial degradation of phenanthrene in soil.

Because phenanthrene was mineralized more slowly in soils than in liquid media, a study was conducted to determine the environmental factors that may account for the slow biodegradation in soil. Mineralization was enhanced by additions of phosphate but not potassium, and it was reduced by additions of nitrate. Aeration or amending the soil with glucose affected the rate of mineralization, although not markedly. Phenanthrene was sorbed to soil constituents, the extent of sorption being directly related to the percentage of organic matter in the soil. Soluble phenanthrene was not detected after addition of the compound to a muck soil. The rate of mineralization was slow in the organic soil and higher in mineral soils with lower percentages of organic matter. We suggest that sorption by soil organic matter slows the biodegradation of polycyclic aromatic hydrocarbons that are otherwise readily metabolized.

Cassava starch effluent treatment with concomitant SCP production.

Yeasts and yeast-like organisms were chosen for the aerobic treatment of cassava starch factory effluent. A mixed culture of Candida utills and Endomycopsis fibuliger efficiently and rapidly utilized both starch and free sugars. After 28 h fermentation the protein content of the biomass was 22% (w/w), which remained unchanged during the remainder of the fermentation (60 h). This treatment removed 94% of the COD and 91% of the BOD.

Anaerobic digestion of cassava starch factory effluent.

Biomethanation of cassava starch factory effluent in a batch digester produced 130 l biogas/kg dry matter with an average melthane content of 59%. About 63% COD was removed during 60 days. In semicontinuous digesters, gas production was 3251/kg dry matter with a retention time of 33,3 days giving a COD reduction of 50%. Size of starter inoculum was important for good biogasification of the effluent.