Toxicity Studies in a Tobacco Industry Biological Treatment Plant

Tobacco industry wastewater contains some toxic contaminantswhich inhibit the microbial consortium in biological treatmentplants. Investigations carried out showed that the most important sources of these toxic contaminants are nicotine,flavoring chemicals containing glycogen and alcohol, absorbableorganic halogens (AOX), and pesticides from tobacco leaves. Shock loadings of these toxic contaminants inhibit the bacterialactivity during biological treatment. Input of wastewater containing such toxic substances causes decreases in bacteria numbers and reduce the treatment efficiency in the treatmentplant. Viable numbers of floc forming, total and faecal coliform bacteria which are living in a biological treatmentunit (i.e. Biopac) were monitored. Conventional short-term bioassays and enrichment toxicity tests were performed to determine potential toxicity. If the ratio of bacteria numbersgrowing in the enrichment medium compared to control is between0.8 and 1.2, it may be assumed that toxic substances are absent.If this ratio exceeds 1.2, it may be assumed that growth stimulating substances are present. If this ratio is below 0.8,this indicates the presence of toxic substances. The results ofenrichment toxicity studies showed that enough nutrients canstimulate the bacterial growth, or known/unknown sources of toxicity can be inhibit the microbial growth. Furthermore, results of chemical coagulation/flocculation test experimentsshowed that chemical treatment is effective at reducing toxicityand is proposed for biological treatment.