Effect of Digested Sewage Sludge on the Ventilation and Coughing Rates of Two Fresh Water Fish

Addition of digested sewage sludge at concentrations of 2% and 10% (v/v) to the water increased coughing rate in big head and tilapia (P<0.05). Ventilation rate was significantly decreased (P<0.05) in big head and tilapia at sludge concentrations of 6% and 2% (v/v)respectively. Copper (Cu), cadmium (Cd) and zinc (Zn) are trace metals which are commonly found in sludge. Cu caused a significant increase (P<0.05) in coughing rate in both tilapia and big head at concentrations of 0.3 and 0.2 μg/ml respectively. Zn caused significant increase (P<0.05) in coughing rate only in big head at 2 μg/ml. Neither fish responded to Cd of up to 2μg/ml in the water. However, when the levels of these trace metals in the digested sludge were measured, they were below that which can cause significant changes in the respiratory movements. Therefore, the changes in ventilation and coughing rates after addition of sludge may be due to the presence of substances other than these metals. The results of this experiment provides a guideline to control the level of sludge that can be used in rearing these fresh water fish in ponds

Determination of the archaeal and bacterial communities in two-phase and single-stage anaerobic systems by 454 pyrosequencing

2-Phase anaerobic digestion（AD）, where the acidogenic phase was operated at 2 day hydraulic retention time（HRT） and the methanogenic phase at 10 days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD（also operated at 12 days HRT）. 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24%of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system＇s performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process.