Avaliação de duas estratégias de partida em biodigestores do tipo CSTR utilizando lodos de sistemas de tratamento de efluentes da suinocultura

Abstract

The swine production has great economic importance in Brazil, with a growing demand in swine production, considering swine meat is one of the most consumed in the world. As the production increases, consequently a higher volume of waste is generated with elevated concentration of nutrients with high polluting hazard for the environment. When the sludge generated by swine production is properly management, it presents great economical value, since it may be used in the generation of biogas and its digestate is a potent biofertilizer. Treatment systems of swine sludge using anaerobic digestion are effective in removing the carbon found in the swine manure. For the effluents treatment, the biodigester is one of the most used technology, because it reduces the organic load. However, the biodigester start up is extremely important for a successful outcome of the whole anaerobic digestion process where required operational controls. The study objective was to evaluate two different strategies to get the continuous stirred (CSTR) biodigester start up, under unfavorable conditions for the anaerobic digestion process initiation by the absence of the acclimatized inoculum, in mesophilic temperature conditions, using sludge from treatment steps of swine production effluents and to evaluate how much the production efficiency and quality of biogas generated from distinguished ways to start up the anaerobic biodigester. The start up strategies studied, named Start up with Substrate (PCS) and Start up without Substrate (PSS), were divided in two stages. In Step I it was analyzed the reactor starting part using only two substrates (rotary sieve sludge and lagoon covered biodigester sludge), as Step II was marked to add of a third substrate the aerobic biological reactor sludge (RBA)in the process. The PSS reactor showed better conditions of operation and stability in the process of anaerobic digestion, therefore, it was decided to only add to this reactor substrate sludge RBA, in order to evaluate the behavior of the anaerobic digestion process with the addition of nitrate, remained the PCS reactor under to operating conditions of Step I. The studied strategies have shown to be efficient for the anaerobic digestion process, in Step I the PCS reactor presented greater operational instability, in contrast obtained faster biogas generation, on the second day it was observed biogas production with 21.0 LN.d-1 and biogas yield (RB) of 1.32 LN biogas g SV adic-1. The ammonia concentration presented high values at the PCS start up, in the range of 233.8 ± 85.0 N-NH3 mg L-1 and the methane quality was established in the range of 56.0 ± 6% (v v-1) in this reactor. In the PSS reactor the highest biogas productivity occurred within 41 days, with values of 0.95 LN biogas Lreator-1 d-1 e RB with 0.78 LN biogas g sv adic-1. On the qPCR analysis has been found species, from the Methanogenic Archaea and Methanobacteriales, Methanosarcinales to Methanomicrobiales orders on the two start-ups studied. The Step II of the experiment marked by the addition of the RBA substrate in the PSS reactor, presented a biogas average production of 6,7 LN d-1, this result demonstrated the COV reduction influence and also when added nitrate on anaerobic systems. The present study aimed to contribute to the improvement of the swine activity, with the reduction of sludge in swine treatment systems, minimizing costs in these processes, cooperating with the identification of the parameters of operational instability that may occur in anaerobic digestion, extracting biogas production from this product.