Heating at 100 °C for 5-10 min is a common method for treating wastewater containing recombinant DNA in many bio-laboratories in China. In this experiment, plasmid pET-28b was used to investigate decay efficiency of waste recombinant DNA during thermo-treatment. The results showed that the decay half-life of the plasmid was 2.7-4.0 min during the thermo-treatment, and even heating for 30 min the plasmids still retained some transforming activity. Low pH promoted the decay of recombinant DNA, but NaCl, bovine serum albumin and EDTA, which existed in the most wastewater from bio-laboratories, protected DNA from degradation. Thus, the decay half-life of plasmid DNA may be longer than 2.7-4.0 min practically. These results suggest that the effectiveness of heating at 100 °C for treating waste recombinant DNA is low and a gene pollution risk remains when those thermo-treated recombinant DNAs are discharged into the environment. Therefore other simple and effective methods should be developed. Heating at 100 °C for 5-10 min to treat waste recombinant DNA has potential eco-risk.

The debate on sludge recycling and disposal has been recently a target of growing interest due to the expressed concern about the potential risks of its agricultural use on human health and the environment. This fact has led to revisions in government policy and regulations and many novel treatment processes have been proposed in order to make the recycling and reuse of sewage sludge sustainable. In this work, the use of some pretreatments (alkaline, thermal, and ozonation) combined with conventional anaerobic digestion has been assessed on digested sludge quality in terms of pathogens, dewatering properties, heavy metals, and organic pollutants. All pretreatments proved to be efficient to reach the requirements proposed in the Working Document on Sludge prepared by the European Commission (CEC, Council Directive of 27 April 2000 on Working Document on Sludge--third draft. Brussels: European Commission DG Environment. Retrieved from http://ec.europa.eu/environment/waste/sludge/pdf/sludge_en.pdf, 2000a) and also those established by the U.S. Environmental Protection Agency (EPA, Standards for the disposal and utilization of sewage sludge, part 503. Retrieved from http://www.epa.state.il.us/public-notices/2004/lincoln-trails-mhp/draft-permit.pdf, 1993).