Bacillus cereus liquid fertilizer was produced from Agaricus bisporus industrial wastewater

•Using A. bisporus industrial wastewater as the nature liquid medium of B. cereus to produce microbial fertilizer that can remarkably enhance the yield of Brassica chinensis L.•Compared with real-time fluorescence quantification PCR and plate count method, the total number of living B. cereus in the fermentation broth was analyzed with multispectral imaging flow cytometry, which is simple, low-cost, very visual, and not easy to be affected by reaction conditions.•Optimization of the culture conditions of B. cereus using A. bisporus industrial wastewater was combined Plackett-Burman design, path of the steepest ascent, with Box-Behnken response surface method, which is a very efficient statistical experiment for microbial fermentation. During the Agaricus bisporus canning processes, a large number of water-soluble elements were dissolved into the processing hot water. This study was conducted to use the industrial wastewater of A. bisporus to prepare agricultural microbial fertilizer. In the work, the influence of 6 different liquid fermentation factors on the total biomass of living Bacillus cereus was evaluated with the one-factor-at-a-time method and the Plackett–Burman design. The total biomass of living B. cereus was most influenced by fermentation temperature, shaking speed, and inoculation volume, which were identified as the most critical independent variables for the B. cereus biomass. The approximate ranges of optimal fermentation conditions for the three key factors were identified by the path of steepest ascent. The center point of these factors were 24 ℃ of temperature, 250 rpm of shaking speed and 12 % inoculum amount, respectively. The Box-Behnken design was applied to derive a statistical model for optimizing the three fermentation factors for B. cereus biomass. After further optimizations based on statistical predictions, the optimum fermentation parameters for B. cereus cultured in the A. bisporus industrial wastewater were fermentation temperature of 24.8 °C, shaking speed of 234 rpm, inoculum dose of 12.2 % (v:v, %), industrial wastewater concentration of 4%, initial pH values of 6.5, loading liquid of 60 mL/250 mL, and culture time of 24 h. Culturing with the optimal fermentation conditions resulted in the biomass of B. cereus of 1.35 ± 0.02 × 109 Obj/mL (N = 3), which was consistent with the predicted values (1.32 × 109 Obj/mL) predicted by the corresponding regression models (p < 0.05), and more, was also far higher than that of the s