Comparison of two combined bioelectrochemical and sulfur autotrophic denitrification processes for drinking water treatment

Two combined bioelectrochemical and sulfur autotrophic denitrification (CBSAD) processes for the treatment of nitrate contaminated drinking water were studied in this article, the main difference between the two processes was whether the limestone was packed in the reactor. In these processes, the sulfur denitrification was carried out in the lower part (Sulfur Part) of the reactors while the bioelectrochemical hydrogen denitrification in the upper part (Bioelectrochemical Part). Sulfur Part of one reactor was packed with elemental sulfur and limestone while no limestone was packed in Sulfur Part of the other, the former reactor is referred to as RSL and the latter as RS. The denitrification results of the two reactors were compared under different conditions, from which it can be concluded that the minimum current of RSL was about 2 mA higher than that of RS. However, at the same hydraulic retention time (HRT) and minimum current, the nitrate removal of both reactors was higher than 90% while no nitrite was accumulated in the effluent. Ca2+ concentration in Sulfur Part effluent of RSL was increased because of the packed limestone, which led to the requirement of Ca2+ removal in Bioelectrochemical Part. The effluent sulfate concentration of RSL was higher than that of RS. When current was lower than 3 mA, the effluent pH value of RSL was about 0.6 higher than that of RS. However, the effluent pH of two parts of both reactors was about neutral under optimum operation conditions. The optimum operation condition of RSL was 1.9-4h HRT under 1.5-14 mA minimum current, while that of RSL was 1.9-5 h under 3-16.5 mA. The effluent quality of RS was better than that of RSL.