4. Conclusions
On the one hand, four pre-treatments were evaluated in 21 set of experiments. Previous work at our
laboratory suggested the use of a specific nutrient of mix for guaranteeing a healthy F:M relationship.
These conditions were the key factor for a good performance of the 21 experiment. It was confirmed that
the combination of heat shock and chemical treatment with HCl (for working under a controlled pH level)
enhance the H2 production in the first stage of a two-stage anaerobic digester. Especial attention was
given to the use of MW as the most suitable heat shock pre-treatment. At the moment the 3 most
representative pre-treatment for the full design are: a) MW 5min@800W+pH4 with a H2 yield of
0.96molH2/mol glucose, HOAc and HOBu production by means of 3828mg/L and 681 mg/L
respectively; b) WB 90°C + pH4 with a H2 yield of 0.62mol H2/mol glucose, HOAc and HOBu
production by means of 3224mg/L and 1360 mg/L respectively; c) BES 7mM produced a H2 yield of 0.52
mol H2/mol glucose, HOAc and HOBu production by means of 2128mg/L and 990 mg/L respectively.
For the final implementation of a pre-treatment, a cost-benefit analysis and energy balance should be
performed. Additionally, it was found that the use of selective inhibitor of methanogenesis (e.g. BES) has
to include an environmental impact assessment, since there are not enough studies focused on the
environmental effects of its by-products. On the other hand, the Case Study helped to observe the
operation and energy implication of implementing a pre-treatment and AD in a real case WWTP for the
treatment of sludge. It showed that the energy neutrality could be reached, only if a energy cheaper
system is implemented. As well, the heat output should be used among the neighbors. Other
recommendation would be the installation of a fuel cell, so the electrical output would be larger. This
option should be analyze for the Benchmark plant in Mexico. The selection of technology should consider
the Best Available Technology, the operation cost of the pre-treatment and the legislation background.
These elements will help to “adapt” the technology, especially under the “Mexican context”.
Additionally, an energy balance considering a fuel cell and a two-stage AD for producing H2 should be
consider for the benchmarks and this might be the key for the Mexican government to invest even more