###### Abstract  
The dark brown anaerobic digestion piggery effluent (ADPE) with a large amount of ammonium generally needs high dilution before microalgae cultivation due to its inhibiting effects on algal growth. Due to the strong decolorization of fungi by degrading organic compounds in wastewater, the process-optimization integrated strategy of fungal decolorization of ADPE and subsequent microalgae cultivation with ammonium-tolerant strain may be a more reliable procedure to reduce the dilution ratio and enhance algal biomass production, and nutrient removal from ADPE. This study determined a suitable fungal strain for ADPE decolorization, which was isolated and screened from a local biogas plant, and identified using 26s rRNA gene sequence analysis. Subsequently, ADPE was pretreated by fungal decolorization to make low-diluted ADPE suitable for the algal growth, and conditions of microalgae cultivation were optimized to achieve maximum algal yield and nutrient removal from the pretreated ADPE. The results showed one promising locally isolated fungal strain, Nanchang University-27, which was selected out of three candidates and identified as _Lichtheimia ornata_, presenting a high decolorization to ADPE through fungal pretreatment. Five-fold low-diluted ADPE pretreated by _L. ornata_ was the most suitable medium for the algal growth at an initial concentration of ammonium nitrogen of 380 mg L\({}^{-1}\) in all dilution treatments. Initial optical density of 0.3 and pH of 9.0 were optimal culture conditions for the algal strain to provide the maximum algal yield (optical density = 2.1) and nutrient removal (88%, 58%, 65%, and 77% for the removal rates of ammonium nitrogen, total nitrogen, total phosphorus, and chemical oxygen demand, respectively) from the pretreated ADPE. This study demonstrated that fungal decolorization and subsequent microalgae cultivation could be a promising approach to algal biomass production and nutrient removal from ADPE. bio-digester effluent; fungal decolorization; process optimization; algal growth; nutrient removal +
Footnote †: journal: Applied Sciences  
AD effluent (ADE) from piggery (ADPE), the byproduct of anaerobic microorganism degradation of organics from piggery wastewater, is enriched in high levels of organic and inorganic compounds, heavy metals, antibiotics, and hormones [5]. Microalgae is a group of unicellular organisms with excellent performance in nutrient assimilation and value-added biomass accumulation during growth, widely applied for the treatment of municipal, agricultural, and industrial wastewaters [6; 7; 8; 9; 10], including ADPE [11]. For example, [PERSON] et al. [9] reported that a mixed-culture microalgae showed effective biomass production (3 g L\({}^{-1}\)) and high nutrient removal rates in ADE from dairy wastewater, reaching above 90% of organic compound and nutrient removal. The harvested algal biomass with abundant carbohydrates, lipids, and proteins can be developed for multi-purpose valuable products such as biogas, biofuel, animal feed, and chemicals (e.g., carotenoids, antioxidants, and polyunsaturated fatty acids) [10]. In addition, microalgae were reported to significantly contribute to atmospheric carbon balance by CO\({}_{2}\) fixation and O\({}_{2}\) emission [12]. In recent decades, microalgae-based wastewater remediation has emerged into the limelight in the field of wastewater treatment owing to the above advantages. Some recent studies explored the feasibility of using microalgae for ADPE remediation [13; 14]. However, current barriers to adopting algal cultivation for ADPE treatment are the quite high turbidity (dark brown color) and ammonium (NH\({}_{4}\)+) concentration, inhibiting algal growth [13]. The dark brown ADPE prevents the passage of sunlight through water bodies and thus greatly inhibits photosynthesis for algal growth [15]. High NH\({}_{4}\)+ content easily shifts the chemical equilibrium from NH\({}_{4}\)+ to free ammonia (NH\({}_{3}\)) at high pH during algal photosynthesis [13].