The Influence Of Arsanilic Acid And Cu²⁺ On Anaerobic Digestion Of Pig Manure And Its Mitigation

Arsanilic acid（ASA）and copper ion(Cu²⁺)have been widely used as feed additives to promote animal growth and improve production performance.Most of the two supplemented feed additives is excreted in feces and urine,which affects the biotreatment of livestock and poultry manure.Anaerobic digestion is often used for treatment of livestock and poultry manure,but the residual feed additives usually influence the stabilization of the anaerobic digestion process.In this work,the influence of ASA and Cu²⁺on anaerobic digestion of pig manure was investigated,the interaction of ASA and Cu²⁺and the mechanism that Cu²⁺mitigated the methanogenesis inhibition caused by ASA were explored,and the control of methanogenesis inhibition on account of ASA and Cu²⁺by microaeration and addition of SO₄^2-was studied.（1）The influence of ASA and Cu²⁺on anaerobic digestion of pig manure was investigated.Individual addition of ASA and Cu²⁺severely inhibited the methanogenesis,and approximately 69.54%of ASA was transformed to inorganic arsenic or entered the sludge.Simultaneous addition of ASA and Cu²⁺almost not inhibited the methanogenesis.After one month anaerobic digestion,significant ASA（71.35%）still existed in the solution.The existence of Cu²⁺impeded the transformation of ASA to more toxic inorganic,which might be the mechanism that Cu²⁺mitigated the methanogenesis inhibition caused by ASA.（2）The interation of ASA and Cu²⁺was explored.Under neutral and alkaline conditions,the combination of ASA and Cu²⁺by electrostatic force formed the complex and then led to the static quenching,and the number of binding site was about one.The toxicity test indicated that the biotoxicity of the complex was lower than ASA and Cu²⁺,and the biotoxicity was lowest when ASA and Cu²⁺were mixed at the rate of 1:1.The formation of lower toxic complex was the internal mechanism that Cu²⁺mitigated the methanogenesis inhibition caused by ASA.（3）The control of methanogenesis inhibition on account of ASA and Cu²⁺by microaeration and addition of SO₄^2-was studied.Microaeration and addition of SO₄^2-did not have influence on the methanogenesis inhibition caused by ASA and the degradation of ASA.But when Cu²⁺existed simultaneously,microaeration and addition of SO₄^2-both could mitigate the methanogenesis inhibition and addition of SO₄^2-could reduce the concentration of arsenic and copper in the solution.The addition of SO₄^2-was an effective way to control the methanogenesis inhibition caused by ASA and Cu²⁺.