Tratamento biológico de esgoto e solubilização de lodo como alternativa de recuperação de subprodutos: material carbonáceo e nutrientes

Abstract

The treatment of sewage by activated sludge using sequential batch reactors (RBS) has been reported to be efficient in removing organic matter and nutrients (N and P). However, the metabolic processes involved in biodephosphate and heterotrophic denitrification occur when organic carbon is available in stoichiometric proportions and in conjunction with other factors, such as sludge age and the optimization of the duration of the aerobic, anaerobic and anoxic phases. In this context, the first stage of the work aimed to evaluate the efficiency of two RBS reactors in the biological removal of nutrients from sewage with different concentrations and different cell retention times (TRC) and cycle times. Thus, two experimental systems were operated in parallel, with system 1 concentrated sewage as an influent and system 2 as moderate sewage. In both systems, cycle times of 24 and 8 hours and TRC of 12 and 5 days were used, respectively for reactors R1 and R2. Biodephosphating was performed with better performance in reactor R2, with an average efficiency of 83% when the system was operated with concentrated sewage. On the other hand, the nitrification/denitrification processes were carried out with greater efficiency in the R1 reactor, with an average efficiency of 84% also when the system treated concentrated sewage. In the second stage of the work, the processes of alkaline and enzymatic solubilization of excess sludge from RBS were evaluated by treating concentrated sewage, in two different reaction times (8 and 48 hours). For that, a complete factorial experimental design 2(2-0) (DOE 2(2-0)) was used, applying three replications and having the pre-treatment (enzymatic: 10% lipase. (gST)-1, and alkaline: NaOH, pH=12) and reaction time (8 and 48 hours) as the independent variables, and filtered COD, carbohydrates, proteins, total phosphorus and orthophosphate as dependents. To analyze the statistical difference in the experimental data, analysis of variance (ANOVA) was performed, and the mean values of the parameters evaluated and the Pareto diagram were constructed with a confidence limit of 95%. The respirometry test was also a parameter used to assess the biodegradability of the sludge (control, without pre-treatment and after pre-treatments). It was observed that the sludge solubilization rate increased in both investigated technologies. However, the applied statistical analysis indicated the alkaline pretreatment as the most effective and the reaction time as significantly relevant in the process. For this technology, the metabolized organic matter was increased by 178 and 279 mgDQOf.L-1 for the reaction times of 8 and 48 hours, respectively. Despite the greater efficiency of the alkaline pre-treatment, the enzymatic process showed a higher fraction of COD consumed (COD), indicating a higher biodegradable fraction, possibly due to the organic properties of the enzyme itself.