Immediate one-step lime precipitation and atmospheric carbonation as pre-treatment for low biodegradable and high nitrogen wastewaters: A case study of explosives industry

Abstract

The treatment of some industrial wastewaters is complex, since they usually contain complex non-biodegradable organic compounds or toxic compounds which are not easily treatable. These compounds are not removed by biological treatment in wastewater treatment plants and they may affect the removal of ammonium, nitrate, organic nitrogen by these treatment systems. Therefore, this research proposes a new and innovative low-cost and easy-to-apply pre-treatment to treat low biodegradable and high nitrogen wastewaters, using explosive wastewaters as case study. The pre-treatment is composed by immediate one-step lime precipitation (IOSLM) and atmospheric CO2 carbonation (AC) processes. The novelty of the proposed pre-treatment is based firstly on the use of one reactant (hydrated lime) at high concentrations, added in one step, that produces immediately an abundant and insoluble precipitate able to sweep the organic matter and other contaminants from wastewater in a short time and ensure conditions (pH and Ca2+) for the AC process. Secondly, the AC process uses the sludge produced in IOSLM to keep pH high for longer, allowing ammonia removal while simultaneously the pH is reduced by spontaneous reactions with atmospheric CO2. IOSLM results showed 92.1 %, 98.2 % and 100 % of organic matter, oils and fats, and organic nitrogen removals, respectively, for the optimal hydrated lime dose (7.76 g L−1). In AC process 61 % of ammonium nitrogen was removed and pH reduced to 8.1 in 10 days.