Abstract
Fresh pig urine is unsuitable for microalgae cultivation due to its high concentrations of NH4+-N, high pH and insufficient magnesium. In this study, fresh pig urine was pretreated by dilution, pH adjustment, and magnesium addition in order to polish wastewater and produce microalgae biomass. Chlorella vulgaris was cultured in an in-house-designed light-receiving-plate (LRP)-enhanced raceway pond to treat the pretreated pig urine in both batch and continuous mode under outdoor conditions. NH4+-N and TP in wastewater were detected, and the growth of C. vulgaris was evaluated by chlorophyll fluorescence activity as well as biomass production. Results indicated that an 8-fold dilution, pH adjusted to 6.0 and MgSO4·7H2O dosage of 0.1 mg·L−1 would be optimal for the pig urine pretreatment. C. vulgaris could stably accumulate biomass in the LRP-enhanced raceway pond when cultured by both BG11 medium and the pretreated pig urine. About 1.72 g·m−2·day−1 of microalgal biomass could be produced and 98.20% of NH4+-N and 68.48% of TP could be removed during batch treatment. Hydraulic retention time of 7-9d would be optimal for both efficient nutrient removal and microalgal biomass production during continuous treatment.
Highlights
Intensive pig farming produces a large amount of piggery waste
Pig urine was witnessed rapid growth after days of lag phase, and the biomass density reached to 220.08 mg·L at day 13
The LRP-enhanced raceway pond has been shown to support the robust growth of C. vulgaris
Summary
Intensive pig farming produces a large amount of piggery waste (urine and manure). Bureau of Statistics of the People’s Republic of China has reported that more than 11 million tons of piggery wastewater were directly discharged into the environment in 2014 [1]. Piggery waste has become a major source of pollution in rural areas of China. It releases greenhouse gases and ammonia, and causes eutrophication, algal blooms, as well as soil acidification [2]. The treatment of piggery waste is a continuing environmental issue in china. Anaerobic digestion (AD) has been widely acknowledged as an effective method to process piggery waste, around the world [3]. AD converts complex organic matter in pig manure into biogas
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