Abstract
BackgroundWith the further development of anaerobic digestion, an increasing output of anaerobically digested wastewater (ADW), which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable. Microalgae cultivation offered a potential waste-to-value strategy to reduce the high nutrient content in ADW and obtain high value-added microalgae. However, ADW generally contained a mass of pollutants (suspended solids, competitors, etc.), which could inhibit microalgae growth and even result in microalgae death by limiting light utilization. Thus, it is highly imperative to solve the problem by a novel modified photobioreactor for further practical applications.ResultsFour microalgae species, Scenedesmus dimorphus, Scenedesmus quadricauda, Chlorella sorokiniana, and Chlorella vulgaris ESP-6, were cultivated in the membrane photobioreactor (MPBR) fed with ADW to investigate the efficiency of ammonia and phosphorus removal. The results showed that C. sorokiniana had the best performance for the removal of ammonia and phosphorus from ADW. The highest amount of C. sorokiniana biomass was 1.15 g/L, and the removal efficiency of phosphate (66.2%) peaked at an ammonia concentration of 128.5 mg/L after 9 days’ incubation. Moreover, the MPBR with 0.1 μm membrane pore size had the best ammonia and phosphate removal efficiencies (43.9 and 64.9%) at an ammonia concentration of 128.5 mg/L during 9 days’ incubation. Finally, the continuous multi-batch cultivation of C. sorokiniana was performed for 45 days in MPBR, and higher removal ammonia amount (18.1 mg/day) and proteins content (45.6%) were obtained than those (14.5 mg/day and 37.4%) in an normal photobioreactor.ConclusionIn this study, a novel MPBR not only eliminated the inhibitory effects of suspended solid and microorganisms, but also maintained a high microalgae concentration to obtain a high amount of ammonia and phosphate removal. The research provided a theoretical foundation for the practical application of MPBRs in various wastewater treatment schemes without pretreatment by algae, which could be used as biofuels or protein feed.
Highlights
With the further development of anaerobic digestion, an increasing output of anaerobically digested wastewater (ADW), which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable
Different microalgaes cultivated with ADW in membrane photobioreactor (MPBR) and normal photobioreactor (NPBR) Four microalgae species (S. dimorphus, S. quadricauda, C. sorokiniana, and C. vulgaris ESP-6) were selected to assess the performance of microalgae growth and nutrients uptake in diluted ADW (64.3 mg/L ammonia, 13.1 mg/L phosphate, 0.86 g/L suspended solids) in MPBR and NPBR
All four algae species removed over 75% of the ammonia nitrogen from the MPBR after 9 days of incubation
Summary
With the further development of anaerobic digestion, an increasing output of anaerobically digested wastewater (ADW), which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable. ADW generally contained a mass of pollutants (suspended solids, competitors, etc.), which could inhibit microalgae growth and even result in microalgae death by limiting light utilization. With the further development of anaerobic digestion, an increasing output of ADW, which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable and approximately 385 million tons of liquid waste had been generated by over 30 million methane-generating tanks [1]. UV radiation, membrane filtration, centrifugation, and autoclaved sterilization had been used as a pretreatment methods before ADW was applied as the culture medium for the cultivation of microalgae [6] These processes had numerous disadvantages, including costliness, instability or complexity, and so on [7]
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