Nitrogen dynamics and biological processes in soil amended with microalgae grown in abattoir digestate to recover nutrients.

The use of microalgae for nutrient recovery from wastewater and subsequent conversion of the harvested biomass into fertilizers offers a sustainable approach towards creating a circular economy. Nonetheless, the process of drying the harvested microalgae represents an additional cost, and its impact on soil nutrient cycling compared to wet algal biomass is not thoroughly understood. To investigate this, a 56-day soil incubation experiment was conducted to compare the effects of wet and dried Scenedesmus sp. microalgae on soil chemistry, microbial biomass, CO2 respiration, and bacterial community diversity. The experiment also included control treatments with glucose, glucose + ammonium nitrate, and no fertilizer addition. The Illumina Mi-Seq platform was used to profile the bacterial community and in-silico analysis was performed to assess the functional genes involved in N and C cycling processes. The maximum CO2 respiration and microbial biomass carbon (MBC) concentration of dried microalgae treatment were 17% and 38% higher than those of paste microalgae treatment, respectively. NH4+ and NO3- released slowly and through decomposition of microalgae by soil microorganisms as compared to synthetic fertilizer control. The results indicate that heterotrophic nitrification may contribute to nitrate production for both microalgae amendments, as evidenced by low amoA gene abundance and a decrease in ammonium with an increase in nitrate concentration. Additionally, dissimilatory nitrate reduction to ammonium (DNRA) may be contributing to ammonium production in the wet microalgae amendment, as indicated by an increase in nrfA gene and ammonium concentration. This is a significant finding because DNRA leads to N retention in agricultural soils instead of N loss via nitrification and denitrification. Thus, further processing the microalgae through drying or dewetting may not be favorable for fertilizer production as the wet microalgae appeared to promote DNRA and N retention.

Lactic acid production from food waste at an anaerobic digestion biorefinery: effect of digestate recirculation and sucrose supplementation.

Low lactic acid (LA) yields from direct food waste (FW) fermentation restrict this production pathway. However, nitrogen and other nutrients within FW digestate, in combination with sucrose supplementation, may enhance LA production and improve feasibility of fermentation. Therefore, this work aimed to improve LA fermentation from FWs by supplementing nitrogen (0-400 mgN·L-1) as NH4Cl or digestate and dosing sucrose (0-150 g·L-1) as a low-cost carbohydrate. Overall, NH4Cl and digestate led to similar improvements in the rate of LA formation (0.03 ± 0.02 and 0.04 ± 0.02 h-1 for NH4Cl and digestate, respectively), but NH4Cl also improved the final concentration, though effects varied between treatments (5.2 ± 4.6 g·L-1). While digestate altered the community composition and increased diversity, sucrose minimised community diversion from LA, promoted Lactobacillus growth at all dosages, and enhanced the final LA concentration from 25 to 30 g·L-1 to 59-68 g·L-1, depending on nitrogen dosage and source. Overall, the results highlighted the value of digestate as a nutrient source and sucrose as both community controller and means to enhance the LA concentration in future LA biorefinery concepts.

Ammonia stress on a resilient mesophilic anaerobic inoculum: Methane production, microbial community, and putative metabolic pathways.

Short term inhibition tests, 16S rRNA tag sequencing and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt), were employed to visualise the effects of increasing total ammoniacal nitrogen (TAN) concentration (3400-10166 ppm TAN) on microbial community structure and metabolic pathways for acetate degradation. The rate of methane production on acetate was significantly reduced by TAN concentrations above 6133 ppm; however, methane continued to be produced, even at 10166 ppm TAN (0.026 ±â€¯0.0003 gCOD.gVS-1inoculum.day-1). Hydrogenotrophic methanogenesis with syntrophic acetate oxidation (SAO) was identified as the dominant pathway for methane production. A shift towards SAO pathways at higher TAN concentrations and a decrease in the number of 'gene hits' for key genes in specific methanogenesis pathways was observed. Overall, the results highlighted potential for inhibition activity testing to be used together with PICRUSt, to estimate changes in microbial metabolism and to better understand microbial resilience in industrial AD facilities.