Treated sewage is a promising source of nitrogen and phosphorus in microalgae biomass production for carbon-neutral biofuel and chemical products. In this study, Chlorella vulgaris was continuously cultivated in membrane photobioreactors (MPBRs) under short hydraulic retention times (HRTs) and with different numbers of submerged membrane modules to investigate potential microalgae productivity when treated sewage was used as a nutrient source. Microalgae biomass concentrations were independent of HRT in MPBRs with one membrane module owing to microalgae biomass deposition on the membrane. Installation of an additional submerged membrane module effectively reduced deposition on the submerged membrane, resulting in increased microalgae biomass concentration and volumetric productivity. Growth kinetics suggested that HRT is the essential parameter influencing the volumetric productivity of microalgae under nutrient-limited conditions, and that optimization of the biomass concentration, which depends on the surface/volume ratio of the photobioreactor and initial light intensity, is critical to maximization of the volumetric productivity under light-limited conditions.
Lake Inba, which serves as a drinking water source in Chiba Prefecture, Japan, has not complied with the environmental standard for COD (3 mg/L) since the 1970s. The high level of dissolved organic matter (DOM) caused by eutrophication in the lake has risen the concern of water treatment. To understand the compositions and sources of DOM in Lake Inba, this study compared molecular compositions of low molecular weight DOM (LMW-DOM, <1 kDa) in the lake and a major river flowing to the lake. Water samples were collected from Lake Inba and Kashima River in June 2015. After solid-phase extraction, LMW-DOM was analyzed by Orbitrap mass spectrometry coupled with electrospray ionization. Based on the accurate mass data, 1,263 and 1,393 molecular formulae were assigned for the lake and river samples, respectively. Among them, 1,193 formulae were shared between the lake and the river, indicating that Kashima River was the representative source of LMW-DOM in the lake at the sampling occasion. Elemental composition of molecular formula demonstrated that 61% of the shared formulae were composed of carbon, hydrogen and oxygen. Hydrogen to carbon ratio and oxygen to carbon ratio of these common molecules were similar to the fingerprints of lignin and tannin.
In this study, nickel hydroxide containing cobalt as a co-precipitation hydroxide (NiCo91) was granulated with a binder (polyethylene terephthalate, PET) and characterized (scanning electron microscopy, specific surface area, amount of hydroxyl groups, and surface pH). In addition, the phosphate ion adsorption capability of the granulated adsorbent was evaluated by examining the effects of contact time and solution pH, analysis of adsorption isotherms, and a desorption study. It was confirmed that NiCo91 calcined at 270°C could be granulated using a PET binder. The specific surface area (32 m2/g) and hydroxyl group amount (0.19 mmol/g) of PET20S (20% binder content and < 500 μm particle diameter) were greater than those of other adsorbents. The amount of the adsorbed phosphate ions was greater for PET20S than that for other adsorbents, indicating that the adsorbent surface properties were related to the adsorption of phosphate ions. The phosphate ions adsorbed onto PET20S could be desorbed by different concentrations of sodium hydroxide, and at least three-fold increase in adsorption/desorption onto PET20S could be obtained. The results show that PET20S is highly promising as a renewable adsorbent of phosphate ions from aqueous solutions.