Treatment of a sanitary landfill leachate using combined solar photo-Fenton and biological immobilized biomass reactor at a pilot scale

A solar photo-Fenton process combined with a biological nitrification and denitrification system is proposed for the decontamination of a landfill leachate in a pilot plant using photocatalytic (4.16 m2 of Compound Parabolic Collectors – CPCs) and biological systems (immobilized biomass reactor). The optimum iron concentration for the photo-Fenton reaction of the leachate is 60 mg Fe2+ L−1. The organic carbon degradation follows a first-order reaction kinetics (k = 0.020 L kJUV−1, r0 = 12.5 mg kJUV−1) with a H2O2 consumption rate of 3.0 mmol H2O2 kJUV−1. Complete removal of ammonium, nitrates and nitrites of the photo-pre-treated leachate was achieved by biological denitrification and nitrification, after previous neutralization/sedimentation of iron sludge (40 mL of iron sludge per liter of photo-treated leachate after 3 h of sedimentation). The optimum C/N ratio obtained for the denitrification reaction was 2.8 mg CH3OH per mg N–NO3−, consuming 7.9 g/8.2 mL of commercial methanol per liter of leachate. The maximum nitrification rate obtained was 68 mg N–NH4+ per day, consuming 33 mmol (1.3 g) of NaOH per liter during nitrification and 27.5 mmol of H2SO4 per liter during denitrification. The optimal phototreatment energy estimated to reach a biodegradable effluent, considering Zahn–Wellens, respirometry and biological oxidation tests, at pilot plant scale, is 29.2 kJUV L−1 (3.3 h of photo-Fenton at a constant solar UV power of 30 W m−2), consuming 90 mM of H2O2 when used in excess, which means almost 57% mineralization of the leachate, 57% reduction of polyphenols concentration and 86% reduction of aromatic content.

► The solar photo-Fenton process was found to be very efficient in the treatment of leachates, enhancing the biodegradability of the leachate and making possible a subsequent treatment by a biological oxidation process.
► Solar energy is an important natural resource and using it in advanced oxidation processes is probably one of the best ways to make the detoxification of leachates from sanitary landfills economically attractive.
► Biological nitrogen removal was achieved by a by two-step process: aerobic nitrification of ammonia to nitrite and then to nitrate followed by anoxic denitrification of nitrate to nitrite, nitric oxide, nitrous oxide and nitrogen gas using an external carbon source.