Effect of magnetite supplementation on mesophilic anaerobic digestion of phenol and benzoate: Methane production rate and microbial communities.

Anaerobic sequential batch tests treating phenol and benzoate were conducted to evaluate the potential of magnetite supplementation to improve methanogenic degradation of phenol and benzoate, and to identify active microbial communities under each condition. Specific CH4 production rates during anaerobic digestion were 218.5 mL CH4/g VSS/d on phenol and 517.6 mL CH4/g VSS/d on benzoate. Magnetite supplementation significantly increased methanogenic degradation of phenol by 9.0-68.0% in CH4 production rate, and decreased lag time by 7.9-48.0%, with no significant reduction in CH4 yield. Syntrophorhabdus, Sporotomaculum, Syntrophus, Syntrophomonas, Peptoclostridium, Soehngenia, Mesotoga, Geobacter, Methanosaeta, Methanoculleus, and Methanospirillum were revealed as active microbial communities involved in anaerobic digestion of phenol and benzoate. Magnetite-mediated direct interspecies electron transfer between Geobacter, Peptoclostridium, and Methanosaeta harundinacea could contribute to this improvement.

Magnetite as an enhancer in methanogenic degradation of volatile fatty acids under ammonia-stressed condition.

Anaerobic batch tests with a 22 full-factorial design of ammonia (1.5, 6.5 g N/L) and magnetite concentrations (0, 20 mmol/L) were conducted separately for methanogenic degradation of acetate, propionate, and butyrate (volatile fatty acids (VFAs)) to 1) quantify the effect of magnetite as an enhancer in methanogenic degradation of each of the VFAs in conditions without ammonia stress (1.5 g N/L) and with ammonia stress (6.5 g N/L), and 2) identify methanogenic consortia that are related to such enhancement. Among the three VFAs, methanogenic degradation of propionate was the least feasible (57% lower specific methanogenic activity RCH4 and three times longer lag time λ than acetate degradation). At low ammonia concentration, only propionate showed improvement in RCH4 (46%) with supplementation of magnetite. In the ammonia-stressed condition without magnetite, RCH4 decreased by 38-58% and λ increased 2.2-8.8 times for all VFAs; magnetite supplementation significantly alleviated these effects. These results demonstrate that magnetite supplementation effectively increases methanogenic degradation of the VFAs even under ammonia-stressed conditions. 16S metagenomic sequencing revealed that distinctive methanogenic consortia were active in the different combinations of substrate, ammonia and magnetite. Alkaliphilus, Hyphomonadaceae SWB02 and Clostridia DTU014, Clostridia D8A-2, Christensenellaceae R-7 group and Rikenellaceae DMER64 were identified as potential syntrophic bacteria that can establish magnetite-mediated direct electron transfer with methanogens (Methanosaeta concilii, Methanosaeta harundinacea, Methanolinea tarda, Methanoculleus bourgensis and Methanosarcina spp.) during methanogenic degradation of VFAs. The results may be useful as a reference to develop effective strategies using magnetite supplementation to remediate anaerobic digestion processes that have been afflicted by VFA accumulation and ammonia inhibition.

Nutrient Recovery of Starch Processing Waste to Cordyceps militaris: Solid State Cultivation and Submerged Liquid Cultivation.

This study demonstrated the potential for managing starch processing waste (SPW) by bioconversion to Cordyceps militaris mycelia using solid state cultivation (SSC) and submerged liquid cultivation (SLC). The growth characteristics of C. militaris mycelium were accessed and compared for SSC and SLC systems on SPW under various conditions of initial SPW concentration, pH, and operating temperature. To quantify the mycelial biomass in SLC, original primer sets targeting the 18S rRNA gene of C. militaris were developed. In SSC, a maximum mycelial growth rate (543.1 mm(2)/day) was predicted to occur at 25.6 g SPW/L, pH 5.5, and 23.8 °C. In SLC, a maximum mycelial growth rate (1918.6 mg/L/day) was predicted to occur at 35.5 g SPW/L, pH 5.5, and 22.0 °C. Temperature was suggested as the most significant factor in both systems. The higher optimum substrate concentration observed for SLC than for SSC was likely due to difference in mycelial morphology and mixing effect.