Coagulation treatment of swine wastewater by the method of in-situ forming layered double hydroxides and sludge recycling for preparation of biochar composite catalyst

Abstract

In order to achieve enhanced treatment of swine wastewater as well as resource recycle, in this work, we applied coagulation treatment on swine wastewater by adding Fe and Mg ions, MgFe layered double hydroxides (LDHs) was yielded during coagulation process and the coagulation sludge was recycled to prepare biochar composite catalyst. The removal rates of total phosphorus (TP) and chemical oxygen demand (COD) by Mg-Fe coagulation could achieve 82.55% and 98.51%, which is higher than that by coagulation with individual Mg2+ or individual Fe3+. Finely dispersed MgFe-LDHs flocculation was formed during the coagulation process and was embedded within zoogloea, suspended particles, organic matters, etc. The obtained coagulation sludge was recycled to prepare biochar composite catalyst by oxygen-limited pyrolysis. Redox reaction of iron compounds and electron shuttles capacity of biochar in the catalyst could activate potassium peroxymonosulfate (PMS) to generate ·OH, ·OOH and 1O2, which was responsible for catalysis potential. The as-prepared biochar composite catalyst showed satisfactory catalytic degradation capacity on tylosin and rhodamine B (pH value varied from 3 to 10), and the maximum degradation rate achieved 92.2% for tylosin and 81.9% for rhodamine B (RhB). Coagulation treatment of swine wastewater and in-situ formed layered double hydroxides recycling was suitable in wastewater treatment and resource recycling, of which the degradation rates of RhB were above 83% after five cycling experiments. In general, the combined process exhibits great potential for the deep treatment of swine wastewater and resource recycling for sludge.