Comparison of Anaerobic Reactors for Electricity Production in PILOT Scale from Vinasse

COMPARISON OF ANAEROBIC REACTORS FOR ELECTRICITY PRODUCTION IN PILOT SCALE FROM VINASSE

André Felipe de Melo Sales Santos1,2, Maurício Alves da Mota Sobrinho2, Adrianus Cornelius van Handel3

1Cetrel S.A.

2Environmental Process and Technology Group – DEQ – UFPE

3Department ofCiviland Environmental Engineering - UFCG

Among the liquid effluents of the sugarcane industry, the vinasse is which has higher pollution potential. In terms of BOD value ranges can range from 15,000 to 50,000 mg.L-1, and its production in conventional distilleries can reach 10-18 L of vinasse per liter of ethanol produced, according to the process and quality of sugarcane. The high amounts of biodegradable organic matter in the raw vinasse indicate its potential for use in biological processes using more rationally this energetic potential. One of the most promising technologies is the anaerobic digestion, which produces methane that can be applied in decentralized generation of electric power or burning processes in the unit. In this work three models of anaerobic reactors were evaluated in pilot scale, verifying the increase of the volumetric organic load on the stability of the reactor in its ability to withstand shock loading and its repercussion on the quality of the biogas generated. Were compared to the UASB reactor (R-11) two other models of anaerobic reactors: reactor IC (internal circulation) (R-21) and reactor (external settler) (R31) that present changes in concept and design in relation to reactor UASB.The reactors were built in fiberglass, in a cylindrical shape with a diameter of 1 m and 4m height (working volume 3.5 m3). Was utilized industrial granular anaerobic sludge of high activity (SMA = 0.7 kg.COD.CH4/kg.VTS.d) as inoculum to reduce the adaptation time of the anaerobic microbiotafor vinasse. As alkalizing, was made use of agronomic urea in aqueous solution, dosed at the entrance of the reactor by a metering pump. Recirculation of treated effluent (of the order of 1:3) was also used to reduce the consumption of alkalizing the use of alkalinity generated in the reactor.The criterion of stability and load increase was the maintenance of the relationship TA/VFA around 3.5 -. 4.0 with load increments of 0.5 to 1.0 kg.COD/m3.d until it reaches the design load of 20 kg COD.m3/d. The reactors operated continuously for 2 consecutive harvest seasons, with the first harvest (January 2011) the maximum load was reached only after 6 months for the three reactors, which presented similar behavior. In the first harvest the average removal efficiencies of COD were respectively 75%, 79% and 79% and the concentration of methane in the biogas on average 88%, 84%, 84% for R-11, R-21 and R-31 reactors, respectively. In the second harvest (August 2011 to April 2012) the maximum load was achieved in only 1 month.This rapid staggering load is due, probably,the adaptation of anaerobic sludge to the vinasse,reducing by one sixth the time required in the previous harvest. The average removal efficiencies of COD were respectively 85%, 87% and 88% and the concentration of methane in the biogas was on average 82%, 65%, 77% for R-11, R-21 and R-31 reactors, respectively in the second harvest. It was found that, in terms of applied load,that the second season the R-21 and R-31 reactors exceeded the design load reaching 30 kg COD.m3/d,however for the reactor R-11 reached only the load of 25 kg.COD.m3/d.Despite this load shedding, the reactor R-11 proved to be robust shown very satisfactory performance with respect to COD removal efficiency, stability and quality of the generated biogas (high methane content). Compared to the other two models tested, although these present technological improvements over contact sludge-substrate and sludge retention, the UASB technology was adequate for the treatment of vinasse, with lower cost to other models of anaerobic reactors studied.

Key-words: Biogas, Vinasse, UASB, internal circulation anaerobic reactor, external settler anaerobic reactor.