Abstract
Biogas slurry has become a serious pollution problem and anaerobic digestion is widely applied to pig manure treatment for environmental protection and energy recovery. To evaluate environmental risk of the emission of biogas slurry, luminescent bacteria (Vibrio fischeri), larvae and embryos of zebrafish (Danio rerio) were used to detect the acute and development toxicity of digested and post-treated slurry. Then the ability of treatment process was evaluated. The results showed that digested slurry displayed strong toxicity to both zebrafish and luminescent bacteria, while the EC50 for luminescent bacteria and the LC50 for larvae were only 6.81% (v/v) and 1.95% (v/v) respectively, and embryonic development was inhibited at just 1% (v/v). Slurry still maintained a high level of toxicity although it had been treated by membrane bioreactor (MBR), while the LC50 of larvae was 75.23% (v/v) and there was a little effect on the development of embryos and V. fischeri; the results also revealed that the zebrafish larvae are more sensitive than embryos and luminescent bacteria to pig slurry. Finally, we also found the toxicity removal rate was higher than 90% after the treatment of MBR according to toxicity tests. In conclusion, further treatment should be used in pig slurry disposal or reused of final effluent.
Highlights
Due to limited fossil energy resources, renewable bio-energy technologies are regarded as alternative of fossil fuels in the future [1,2]
If the inhibition of luminescence intensity for V. fischeri, hatching rate for zebrafish embryos, mortality for zebrafish larvae were lower than 50% and malformation rate for zebrafish embryos was lower than 50% exposed to pig slurry, it showed lethal concentration 50 (LC50) (EC50) couldn’t be calculated, toxicity unit (TU) was calculated according to the formula as in Equation (2) [27]: TU RE 100 0.02 (2)
It showed that pollutants in the pig slurry were reduced mostly after the treatment of membrane bioreactor (MBR), where the value of NH3-N and COD
Summary
Due to limited fossil energy resources, renewable bio-energy technologies are regarded as alternative of fossil fuels in the future [1,2]. Biogas based on methane fermentation is becoming an attractive energy resource in many nations worldwide [3]. In China, there are more than 1.5 × 104 biogas projects based on livestock and poultry breeding [4], which was expected to alleviate the energy shortage and reduce the emission of the waste. It still poses environmental risk in biogas project even slurry was successfully anaerobically digested. Recent research has focused on treatment methods for slurry, which could be potential requirement of the risk evaluation of slurry, especially toxicity
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