Heng Li

Nitrogen and phosphorus removal coupled with carbohydrate production by five microalgae cultures cultivated in biogas slurry.

In this study, five microalgae strains were cultured for their ability to survive in biogas slurry, remove nitrogen resources and accumulate carbohydrates. It was proved that five microalgae strains adapted in biogas slurry well without ammonia inhibition. Among them, Chlorella vulgaris ESP-6 showed the best performance on carbohydrate accumulation, giving the highest carbohydrate content of 61.5% in biogas slurry and the highest ammonia removal efficiency and rate of 96.3% and 91.7mg/L/d respectively in biogas slurry with phosphorus and magnesium added. Additionally, the absence of phosphorus and magnesium that can be adverse for biomass accumulation resulted in earlier timing of carbohydrate accumulation and magnesium was firstly recognized and proved as the influence factor for carbohydrate accumulation. Microalgae that cultured in biogas slurry accumulated more carbohydrate in cell, making biogas slurry more suitable medium for the improvement of carbohydrate content, thus can be regarded as a new strategy to accumulate carbohydrate.

Effectiveness and mechanisms of ammonium adsorption on biochars derived from biogas residues

The solid by-product of anaerobic digestion derived biochar has been used as an adsorbent for the liquid by-product and is a viable and environmental friendly way to control waste. In this study, two biochars (BC-PM, BC-ST) from pig manure biogas residue (BR-PM) and straw biogas residue (BR-ST) were assessed for ammonium adsorption. The ammonium adsorption on both BC-PM and BC-ST followed the Elovich kinetic model and fit well with the Langmuir isotherm, whereas BC-PM was better than BC-ST at absorbing ammonium. In addition, the adsorption mechanism was elucidated by analysing the physicochemical properties of the biochars. The Brunauer–Emmett–Teller (BET) surface area, pore structure and micromorphology, which are mainly related to the carbon in the biochars, had no direct correlation with the ammonium adsorption capacity. However, the ash in the biochars played an important role in ammonium adsorption. The metal elements in biochar ash significantly decreased after adsorption, especially potassium, which nearly disappeared as a result of ion exchange with ammonium. However, the quartz and carbonate mineral in biochar ash also functioned as ammonium adsorption sites according to Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis. This study revealed the irreplaceable role of ash in biochars for ammonium adsorption, which will guide the preparation of biochars from different types of feedstocks for ammonium adsorption.

Synthesis of short-chain-length and medium-chain-length polyhydroxyalkanoate blends from activated sludge by manipulating octanoic acid and nonanoic acid as carbon sources

The effects of octanoic acid/nonanoic acid and acclimation time on the synthesis of short-chain-length and medium-chain-length PHA blends from activated sludge were investigated. An increased concentration (847-1366 mg/L) of PHAs resulted from 4-month acclimation compared with the concentration derived from 2-month acclimation (450-1126 mg/L). The content of octanoic acid had a positive linear relationship with the content of even-numbered carbon monomers among the PHAs. The blending products were identified mainly with scl-PHAs during the 2-month acclimation period and were thereafter dominated by mcl-PHAs until 4 months of acclimation. Thermal properties analysis demonstrated that the products derived from 4-month acclimation were a mixture of scl-PHAs and mcl-PHAs rather than a copolymer of scl-PHAs and mcl-PHAs. High-throughput sequencing results indicated that Pseudofulvimonas, Paracoccus, and Blastocatella were the dominant genera that might be responsible for scl-PHAs production during the 2-month acclimation period, whereas Comamonas and Pseudomonas that were responsible for mcl-PHAs production then became the dominant genera after 4-months acclimation.

Nitrogen and phosphorus removal from anaerobically digested wastewater by microalgae cultured in a novel membrane photobioreactor

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 1.15xa0g/L, and the removal efficiency of phosphate (66.2%) peaked at an ammonia concentration of 128.5xa0mg/L after 9xa0days’ incubation. Moreover, the MPBR with 0.1xa0μm membrane pore size had the best ammonia and phosphate removal efficiencies (43.9 and 64.9%) at an ammonia concentration of 128.5xa0mg/L during 9xa0days’ incubation. Finally, the continuous multi-batch cultivation of C. sorokiniana was performed for 45xa0days in MPBR, and higher removal ammonia amount (18.1xa0mg/day) and proteins content (45.6%) were obtained than those (14.5xa0mg/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.