A simple and effective treatment for the safe discharge of concentrated disinfectant solutions

DOUMIC L.I.; RODRIGUEZ G. ; CAPANO A.; FERRO OROZCO A.M.; AYUDE M.A.

Buenos Aires

Congreso; XI World Chemical Engineering Congress; 2023

The use of disinfectants containing Benzalkonium Chlorides (BAC) is widespread and increasingly being released into the environment. BAC concentrations used in hospitals can be as high as 0.1%w/v [1]. This study analyzes the feasibility of treating concentrated BAC solutions by homogeneous Fenton oxidation with subsequent storage. Fenton tests were conducted using BAC 0.1%w/v (1000 mgBAC/L, 2176 mgCOD/L, and 743mgDOC/L) in a batch reactor at pH0=3 and 30°C for 180 min. The storage of Fenton-treated liquids was in the dark, at room temperature, and without stirring. The effect of initial catalyst load ([Fe+2]0=0.36, 1.70 mmol/L), oxidant concentration ([H2O2]0=15, 50, 75, 150 mmol/L) and storage time on the evolution of BAC, oxidant, total dissolved iron (TDI), dissolved organic carbon (DOC), and carboxylic acids concentrations was analyzed. When oxidant was depleted, the chemical oxygen demand (COD) was also measured. The effectiveness of the treatment was evaluated in terms of the impact of the treated solutions on a non-acclimated activated sludge (NAS). In particular, biodegradability, toxicity and susceptibility to antibiotics (Ampicillin, Cephalexin, and Ciprofloxacin) were evaluated and taken as criteria for safe wastewater discharge. The minimum inhibitory concentration (MIC) was recorded as the lowest antimicrobial concentration that prevented any measurable growth.For the tests performed with [Fe+2]0=0.36 mmol/L, H2O2 was completely consumed within 7 days using only [H2O2]0=50 mmol/L, and 96% of BAC conversion was attained. However, the residual solution showed inhibition of respiratory activity (21.4%), evidencing its negative effect on microbial metabolism. For those conducted with [Fe+2]0=1.70 mmol/L, best results were achieved with [H2O2]0=150 mmol/L. BAC conversion was 93.6%, and H2O2 and TDI concentrations were 98.5 and 0.78 mmol/L, respectively. After 4 days of storage, oxidant was depleted and the treated solution (FTSBAC) contained 1.5 mgBAC/L, 426 mgDOC/L, 434 mgCOD/L, and 1.62 mmolTDI/L. TDI profile decreased due to iron precipitation as Fe(OH)3, from 90 to 180 min remained almost constant, and increased during the storage period. 25% of DOC content was due to carboxylic acids. Oxalic, malonic, succinic, formic and acetic acids were detected with a total concentration of 337 mg/L. Both, oxalic (144 mg/L) and malonic (136 mg/L) acids have a strong chelating capacity with Fe(III), and their presence in the reaction medium was responsible for the observed TDI increase. Inhibition of the respiratory activity of the NAS was -62% for FTSBAC and 0% for 1.5 mgBAC/L, indicating an enhancement of the metabolic activity due to the presence of biodegradable intermediate products formed. Indeed, the extent of biological degradation of FTSBAC was 79% in 3 days. In addition, decrease in the MIC of Ciprofloxacin and no effect on the other antibiotic MICs were observed. Results demonstrated this strategy could be a feasible alternative to preserve the biological system and prevent antibiotic resistance development.