Sulfide inhibition to nitrifying bacteria has prevented the integration of digestate nitrification and biogas desulfurization to simplify anaerobic digestion systems. In this study, liquid digestate with NaHS solution was treated using nitrifying sludge in a sequential-batch reactor with a long fill period, with an ammonium loading rate of 293 mg-N L-1 d-1 and a stepwise increase in the sulfide loading rate from 0 to 32, 64, 128, and 256 mg-S L-1 d-1. Batch bioassays and microbial community analysis were also conducted with reactor sludge under each sulfide loading rate to quantify the microbial acclimatization to sulfide. In the reactor, sulfide was completely removed. Complete nitrification was maintained up to a sulfide load of 128 mg-S L-1 d-1, which is higher than that in previous reports and sufficient for biogas treatment. In the batch bioassays, the sulfide tolerance of NH4+ oxidizing activity (the 50% inhibitory sulfide concentration) increased fourfold over time with the compositional shift of nitrifying bacteria to Nitrosomonas nitrosa and Nitrobacter spp. However, the sulfur removal rate of the sludge slightly decreased, although the abundance of the sulfur-oxidizing bacteria Hyphomicrobium increased by 30%. Therefore, nitrifying sludge was probably acclimatized to sulfide not by the increasing sulfide removal rate but rather by the increasing nitrifying bacteria, which have high sulfide tolerance. Successful simultaneous nitrification and desulfurization were achieved using a sequential-batch reactor with a long fill period, which was effective in facilitating the present acclimatization.
Significantly high eicosapentaenoic acid (EPA) and fucoxanthin contents with high production rate were achieved in semi continuous culture of marine diatom. Effects of dilution rate on the production of biomass and high value biocompounds such as EPA and fucoxanthin were evaluated in semi-continuous cultures of Chaetoceros gracilis under high light condition. Cellular dry weight increased at lower dilution rate and higher light intensity conditions, and cell size strongly affected EPA and fucoxanthin contents. The smaller microalgae cells showed significantly higher (p < 0.05) value of 17.1 mg g-dw-1 fucoxanthin and 41.5% EPA content per total fatty acid compared to those observed in the larger cells. Chaetoceros gracilis can accumulate relatively higher EPA and fucoxanthin than those reported previously. In addition, maintenance of small cell size by supplying sufficient nutrients and light energy can be the key for the increase production of valuable biocompounds in C. gracilis.