Solubilização de material carbonáceo e nutrientes de lodo aeróbio através do pré-tratamento químico

Abstract

Chemical solubilization is a non-physical sludge treatment technology which combines several techniques that have in common the addition of an organic or inorganic species able to degrade the microbial aggregates, structured and protected by extracellular polymeric substances (EPS), through depolymerization. This action directly implies the polymeric structure disruption causing cell lysis. It reduces the inner floc mass and increases the fraction of microbial products solubilized. In this research three different strategies of chemical solubilization were investigated: 1) acid and alkaline, using NaOH and HCl the pH was adjusted to 2, 10, 11 and 12 units, and neutralized after the solubilization process; 2) enzymatic with hydrolytic enzymes such as protease and lipase; and 3) solubilization by Dowex® Marathon™ C cation exchange resin in sodium form (Na+), a technique aimed at de-structuring the polymeric substances by changing their electrical charges, it disturbs the attractiveness and repulsion of the flocs constituents. For the three strategies were investigated its effects on the sludge, influence of chemical species concentrations, pH, activity limitation, reaction time and total solids (TS) concentration. Each technique has very particular factors, such as increase in salinity, its purely biological properties, flocculation by protonation and/or deprotonation. Thus, the depolymerization process was confirmed using physico-chemical parameters such as dissolved organic carbon, COD, phosphorus, NTK, TS, proteins and carbohydrates. The microbial products release in the soluble fraction was also confirmed by biological tests with a significant increase of metabolized fraction. Among these parameters, the COD tests associated with respirometry, as well as the analyzes of proteins and carbohydrates, are the ones that best make possible a comparison between the methods. However, it is important to notice that the investigation of TS concentrations (5 mg.L^-1, 10 mg.L^-1, 15 mg.L^-1, 20 mg.L^-1, 25 mg.L^-1 e 30 mg.L^-1), relative to the chemical species dosages, enabled an unpublished conclusion, remotely discussed among the articles in the area, however it is important that the treatment plants are aware that they can increase the concentrations of solids while maintaining the same chemical dosages. The alkaline solubilization efficiency was 456% for filtered COD (DQOf) and 858% for COD used (DQOu), while the enzymatic was 174% DQOf and 874% DQOu, and using resin was 63% DQOf and 134% DQOu. The increase in the recalcitrant soluble fraction was registered for all, the organic chemical species presented superiority in the increase of the fraction metabolized in the biological tests. However, the increase in protein concentration in the soluble fraction gave an efficiency of 3991%, 75% and 236%, for alkaline, enzymatic and cationic solubilization, respectively. Regarding carbohydrates, the efficiency was 1716%, 90% and 283%, respectively for alkaline, enzymatic and cationic. Despite the remarkable alkaline superiority, the enzyme registered a smaller remaining recalcitrant fraction, but it needed to be combined with another treatment to improve its efficiency. The use of the resin was discrete, although the increase of its concentration allows superiority, but its high cost makes this technology unfeasible.