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- Vertical flow constructed wetland as a green solution for low biodegradable and high nitrogen wastewater: A case study of explosives industryPublication . Madeira, Luís Miguel; Carvalho, Fatima; Teixeira, Margarida Ribau; Ribeiro, Carlos; Almeida, AdelaideThe removal of nitrogen compounds from a pretreated explosives wastewater in vertical flow constructed wetland planted with Vetiveria zizanioides (0.24 m(2) x 0.70 m), filled with light expanded clay aggregates (Leca (R) NR 10/20), was studied. Experiments under constant hydraulic load, 50 +/- 4 Lm(-2) d(-1) and 83 +/- 5 L m(-2) d(-1) without and with flooding level (25%), respectively, were made at different ammonium (3-48 mg NH4+-N L-1), nitrate (56-160 mg NO3--N L-1) and nitrite (0.3-1.1 mg NO2--N L-1) concentrations. Results indicate that without flooding level (unsaturated) the removal efficiencies obtained were 30 +/- 9, 7 +/- 1 and 96 +/- 2%, respectively to NH4+-N, NO3--N and NO2--N. When using flooding level and an external carbon source (C/N ratio from 1.3 +/- 0.19 to 2.5 +/- 0.20), the organic matter (COD) removal efficiencies were above 90%, 75% for NH4+-N and 55% to NO3--N. Increasing the C/N ratio from 2.9 +/- 0.21 to 4 +/- 0.22 did not contributed to upgrade the efficiencies of COD, NH4+-N and NO3--N removal. The denitrification process was occurred in aerobic conditions and nitrite production have ben occurred, probably due to the presence of aerobic conditions that inhibited partially denitrification. (C) 2021 Elsevier Ltd. All rights reserved.
- Immediate one-step lime precipitation and atmospheric carbonation as pretreatment for low biodegradable and high nitrogen wastewaters: A case study of explosives industryPublication . Madeira, Luis; Almeida, Adelaide; Ribau Teixeira, Margarida; Prazeres, Ana; Chaves, Humberto; Carvalho, Fatima; Madeira, Luís Miguel SimãoThe 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.