Susana Cortez

Evaluation of Fenton and ozone-based advanced oxidation processes as mature landfill leachate pre-treatments.

Fenton treatment (Fe(2+)/H(2)O(2)) and different ozone-based Advanced Oxidation Processes (AOPs) (O(3), O(3)/OH(-) and O(3)/H(2)O(2)) were evaluated as pre-treatment of a mature landfill leachate, in order to improve the biodegradability of its recalcitrant organic matter for subsequent biological treatment. With a two-fold diluted leachate, at optimised experimental conditions (initial pH 3, H(2)O(2) to Fe(2+) molar ratio of 3, Fe(2+) dosage of 4 mmol L(-1), and reaction time of 40 min) Fenton treatment removed about 46% of chemical oxygen demand (COD) and increased the five-day biochemical oxygen demand (BOD(5)) to COD ratio (BOD(5)/COD) from 0.01 to 0.15. The highest removal efficiency and biodegradability was achieved by ozone at higher pH values, solely or combined with H(2)O(2). These results confirm the enhanced production of hydroxyl radical under such conditions. After the application for 60 min of ozone at 5.6 g O(3)h(-1), initial pH 7, and 400 mg L(-1) of hydrogen peroxide, COD removal efficiency was 72% and BOD(5)/COD increased from 0.01 to 0.24. An estimation of the operating costs of the AOPs processes investigated revealed that Fe(2+)/H(2)O(2) was the most economical system (8.2 € m(-3)g(-1) of COD removed) to treat the landfill leachate. This economic study, however, should be treated with caution since it does not consider the initial investment, prices at plant scale, maintenance and labour costs.

Ozonation as polishing treatment of mature landfill leachate

Mature landfill leachate is typically resistant to biological processes. In order to enhance the biodegradability of a pre-treated mature landfill leachate, ozonation treatments in a lab-scale column were assayed under different ozone concentrations, contact time, initial pH, and hydrogen peroxide concentrations. Degradation of the landfill leachate by ozone was favoured at higher pH values and with the addition of H(2)O(2), both consistent with the enhanced production of the hydroxyl radical under such conditions. The highest organic reduction and biodegradability improvement was observed with the O(3)/H(2)O(2) process at 600 mg H(2)O(2) L(-1). This system was able to remove 63% of chemical oxygen demand (COD), 53% of total organic carbon (TOC), 42% of aromatic content (UV(254)) and increased the leachate 5-day biochemical oxygen demand (BOD(5)) to COD ratio from 0.01 to 0.17. Ozone combined with H(2)O(2) contributed significantly to remove and change the recalcitrant organic matter and improved leachate biodegradability, which makes this process very attractive as pre-biological treatment.

Effect of operating parameters on denitrification in an anoxic rotating biological contactor

The presence of nitrate in water and wastewater is a serious environmental problem. Anoxic rotating biological contactors (RBC) are a promising novel technology for nitrate removal. In this study the effect of two carbon/nitrogen (C/N) molar ratios (1.5 and 3.0) on denitrification, using acetate as a carbon source, were investigated in an anoxic bench‐scale RBC, treating synthetic wastewater. The effect of different hydraulic retention times (HRTs) and different nitrogen and carbon influent concentrations on the reactor performance, at constant C/N, were also analysed. The average removal efficiency in terms of nitrogen‐nitrate was about 90.4% at C/N = 1.5, lowering to 73.7% at C/N = 3.0. Considering carbon‐acetate removal, overall efficiencies of 82.0% and 63.6% were attained at C/N ratios of 1.5 and 3.0, respectively. The increase in nitrogen‐nitrate (from 50 to 100 mg N‐NO3 − L−1) and carbon‐acetate influent concentrations and the decrease in HRT, keeping C/N constant, had a slight negative effect in terms of substrate removal. It was found that, for the tested conditions, the use of C/N = 1.5 is advantageous to denitrification. The anoxic RBC was significantly effective at reducing nitrate concentrations within a relatively short HRT. These reactors may be a feasible option for the treatment of nitrate‐rich wastewaters.