Enhanced biodegradability of UV and VUV pre-treated natural organic matter

A systematic investigation of the effectiveness of utilising UV (254 nm) or VUV (254 nm + 185 nm) photo-oxidation followed by biological treatment for the removal of natural organic matter (NOM) from a sample of drinking water was undertaken. The conditions of UV and VUV pre-treatment required to achieve maximum biological removal were determined. Positive correlations were observed between the production of smaller molecular weight molecules as shown by HPSEC and the decrease in dissolved organic carbon with increasing radiation dose. Similarly, the reduction of UV absorbance at 254 nm was found to correlate well with the observed increase in biodegradability of the UV-treated samples. UV pre-treatment resulted in the accumulation of biodegradable compounds from the breakdown of chromophoric material, although significant concentrations of refractory DOC remained even after the largest dose (140 J.cm⁻²). VUV pretreatment resulted in a rapid rate of mineralisation and fast formation of biodegradable compounds. VUV doses larger than 96 J.cm⁻² were observed to reduce the apparent effectiveness of biological treatment. After the experimentally determined optimal VUV dose, approximately 80% of remaining DOC was biodegradable demonstrating that greater total DOC removal was achieved utilising VUV irradiation followed by biological treatment. The smaller doses of radiation required and greater bioavailability make VUV more effective than UV pre-treatment.