Reduction of toxic products and bioaerosol emission of a combined ultraviolet-biofilter process for chlorobenzene treatment.

A combined process involving ultraviolet (UV) photodegradation and biofiltration was developed to treat gaseous chlorobenzene. The toxicity of the photodegradation products and the bioaerosol emissions from the biofilter were investigated. The experimental results showed that a standalone UV photodegradation of chlorobenzene can result in products having significant acute toxicity and genotoxicity, whereas a biofiltration process can produce a high concentration of bioaerosols, which are a potential health risk. In the combined process, the toxic products produced by the UV photodegradation were removed by the subsequent biofilter. The acute toxicity of the products was reduced from 0.042 to 0.005 mg zinc/mg total organic carbon (TOC). Also the genotoxicity was reduced from 0.76 to 0.16 microg 4-nitroquinoline-N-oxide per milligram TOC. On the other hand, the bioaerosol concentration emitted from the biofilter decreased from 1.38 x 10(3) colony-forming units (CFU) x m(-3) (without UV pretreatment) to 60 CFU x m(-3) (with UV pretreatment), nearly the same as the background level of 40 CFU x m(-3). The significant decrease in bioaerosol emission might be due to a high concentration of ozone (50 mg x m(-3) or 25 parts per million by volume produced by the UV pretreatment. Hence, the UV photodegradation and biofiltration process exhibited synergistic effects. Also, the combined UV-biofiltration process was ecologically safer and exhibited a lower degree of infectivity as compared with standalone UV or biofiltration processes.