This study was carried out to assess the treatment ability of color, dye, and COD in the dyeing wastewater containing C.I Reactive Blue 160 by ozonation system. Both batch and continuous operating modes with concurrent and counter-current flows were investigated. The effects of the ozone gas flow rate, pH, temperature, Na2CO3 concentration, and initial dye concentration were evaluated. The decolorization, dye removal efficiencies, and mineralization ability of COD by ozonation were determined. The results indicated that ozonation had high efficiency in the treatment of dyeing wastewater containing C.I Reactive Blue 160. The treatment performance was affected by the ozone gas flow rate, pH, temperature, Na2CO3 concentration, and initial dye concentration. The removal efficiency of color, dye, and COD were 98.04%, 99.84%, and 87.31% for the treatment of 200 mg/L initial dye concentration in batch mode with 30 min ozonation time, respectively. In the continuous operation and counter-current flow, the color, dye, and COD removal efficiencies reached 97.24%, 99.76%, and 86.38% after 30 min HRT, respectively, and higher than concurrent flow. The reaction of ozone and C. I Reactive Blue 160 was the first-order reaction in both batch and continuous operation. The complete mineralization required 90 min ozonation time.

Cassava (Manihot esculenta) is an important staple crop in Vietnam and is estimated to produce about 10.7 million tons of starch annually. The starch production process generates a large amount of solid waste, namely cassava peels, which are currently disposed of directly into the environment. This practice poses a risk of generating foul odor, attracting disease-carrying organisms, and directly affecting human health. Therefore, reusing cassava peels for growing gray oyster mushrooms is the most appropriate solution. First and foremost, the cyanide content in cassava peels must be treated using the Sun-drying method. Results showed that the cyanide level decreased to the optimal level of 0 mg/kg from 34 mg/kg. After reusing cassava peels to grow gray oyster mushrooms, the results showed that the highest yield was 272 g/bag for cassava peels substrate, while the highest yield for sawdust substrate was 293 g/bag. Statistical evaluations showed that reusing cassava peels to replace sawdust substrate for growing gray oyster mushrooms also resulted in an equivalent yield. Utilizing the substrate after growing mushrooms on cassava peels to grow cabbage produced a germination rate and plant height development equivalent to those grown on commercial fertilizer substrate.