Growth optimisation of microalga mutant at high CO2 concentration to purify undiluted anaerobic digestion effluent of swine manure

•Microalga mutated by nuclear radiation was used to remove pollutants from effluent.•Continuous introduction of 15% (v/v) CO2 supplemented deficient carbon in effluent.•Adding P to effluent and aeration before inoculation improved microalgal growth.•Biomass yield and growth rate were increased to 4.81 g L−1 and 601.2 mg L−1 d−1.•Removal efficiencies of COD, NH3–N and TP from effluent were increased to 73–95%.

Growth rate of the microalga Chlorella PY-ZU1 mutated by nuclear irradiation was optimised for use in the purification of undiluted anaerobic digestion effluent of swine manure (UADESM) with 3745 mg L−1 chemical oxygen demand (COD) and 1135 mg L−1 total nitrogen content. The problem of accessible carbon in UADESM was solved by continuous introduction of 15% (v/v) CO2. Adding phosphorus to UADESM and aeration of UADESM before inoculation both markedly reduced the lag phase of microalgal growth. In addition, the biomass yield and average growth rate of Chlorella PY-ZU1 increased significantly to 4.81 g L−1 and 601.2 mg L−1 d−1, respectively, while the removal efficiencies of total phosphorus, COD and ammonia nitrogen increased to 95%, 79% and 73%, respectively. Thus, the findings indicate that Chlorella PY-ZU1 can be used for effective purification of UADESM, while the biomass can be safely used as animal feed supplement.