Influence of reactive brilliant blue before and after pre-treatment by heterogeneous Fenton-like on characteristics of anaerobic granular sludge

Using reactive brilliant (RB) blue as anthraquinones model pollutants, the inhibition mechanism on methanogenic activity of anaerobic granular sludge was investigated. Likewise, the effect of sludge characteristics on particle size distribution (PSD), metal content and extracellular polymeric substances (EPS) via pre-treatment of heterogeneous Fenton-like oxidation were evaluated. Lastly, degradation pathway of RB blue was proposed. The results showed that RB blue had metabolic or even physiologic toxicity for methanogens. When RB blue was injected into anaerobic reactor, COD removal efficiency was reduced and partical size of anaerobic granular sludge was decreased. Meanwhile, the calcium and magnesium ion concentrations of the granular sludge decreased from 40.5 and 16.2 mg·L^-1 to 22.5 and 6.8 mg·L^-1, respectively. The stability and flocculability of the granular sludge were deteriorated. However, by pre-treatment of heterogeneous Fenton-like oxidation, COD removal efficiency climbed to more than 90%, while the contents of EPS, protein and polysaccharide increased to 98.7, 69.9, and 28.8 mg·(g VSS)^-1, respectively, which guaranteed the favorable stability and activity of the anaerobic granular sludge. The exploration on degradation pathway of RB blue indicated that the hydroxyl free radicals firstly attacked triazine group and anthraquinone structure of RB blue, producing phthalic acid and benzoic acid. After that, they were degraded into small molecule carboxylic acid such as butyric acid, oxalic acid, acetic acid, and so on. The toxicity was reduced, which was beneficial to the anaerobic biological post-treatment.