Codigestão anaeróbia de lixiviado de aterro sanitário com lodo flotado de agroindústria para produção de biogás

Abstract

Sanitary landfill leachate, commonly known as “leachate”, exhibits high diversity and complexity in its pollutant load, making it difficult to apply a single treatment method. To prevent environmental impacts associated with its discharge into water bodies or soil, leachate must undergo complete treatment. In turn, centrifuged floated sludge, an effluent generated in agro industrial wastewater treatment, poses the challenge of being produced in large volumes, resulting in significant costs for disposal and transport to licensed facilities. Due to these characteristics, both effluents motivated the investigation of anaerobic co-digestion for biogas production, fostering the development of sustainable alternatives for treatment and clean energy generation. The objective of this study was to assess the efficiency of organic matter removal and biogas production from sanitary landfill leachate co-digested with centrifuged floated sludge from an agro-industrial complex in batch reactors, aiming at energy recovery. The research was divided into three phases: Phase 1: batch reactor using the Ritter fermentation system; Phase 2: batch reactor in BOD bottles; and Phase 3: batch reactor in a shaker. In all phases, the residues were collected and their physicochemical characteristics analyzed, as well as the mixtures of each reactor before incubation and at the end of the predetermined period. An experimental design was developed for Phases 1 and 2. Eleven reactors were incubated at 37ºC for approximately 60 days or until accumulated biogas production fell below 1%. The pH was adjusted before incubation, according to the central composite rotational design (CCRD), along with the proportions of the studied residues. Statistical analyses were applied to the results, and in Phase 2 it was possible to optimize the model. To validate the optimal point, the parameters obtained were applied to batch reactors operated on a shaker (Phase 3). Phase 1 showed that the test reactor containing centrifuged floated sludge performed better than the reactor with non-centrifuged floated sludge for the response variable (COD removal). Thus, centrifuged floated sludge was selected as the essential co-substrate for the experimental design in Phase 2. In Phase 2, among all reactors in the experimental design, Reactor 6 achieved the highest COD removal (73.73% for centrifuged COD and 84.38% for filtered COD), operating with 95% leachate and pH 7.5. For methane production, the central points of the design showed the highest values, approximately 7.5 L CH₄/L reactor, with parameters of 97.5% leachate and pH 7.5. The reactor containing only leachate (Reactor 5) and the test reactors with only centrifuged floated sludge or distilled water (Reactors 19 and 20) did not show significant results, confirming the advantage of co digestion over mono-digestion. Model optimization indicated 96.3% landfill leachate and pH 7.7 as the optimal independent variables, predicting 6.76 L CH₄/L reactor. After operating the Phase 3 reactor, methane production exceeded expectations, reaching 10.01 L CH₄/L reactor. In conclusion, the co-digestion of sanitary landfill leachate with centrifuged floated sludge from poultry processing contributes to advances in clean and renewable energy research, supporting energy autonomy through biogas production. Finally, for real-scale application, obtaining seasonal operational data from a pilot-scale reactor is recommended to generate a robust database and increase confidence in system design