Algal biomass production by phosphorus recovery and recycling from wastewater using amorphous calcium silicate hydrates.

The phosphorous supply crisis is a major challenge for a sustainable society, and the algal industry is not unrelated to this crisis. Recycling phosphorus from sewage wastewater is a potential way to address this issue. We previously developed amorphous calcium silicate hydrates (aCSH) as excellent phosphorus recovery materials. In this study, we designed a phosphorus recovery process using aCSH in a pilot-scale facility connected to a sewage wastewater treatment plant, and demonstrated the production of microalgal biomass using phosphorous-containing aCSH (P_aCSH). As a result, high phosphorous recovery rates (>80%) were obtained throughout the year. The carbohydrate-rich microalga Pseudoneochloris sp. NKY372003 was cultivable with P_aCSH. The biomass and carbohydrate productivity of this microalga with P_aCSH was comparable to that with conventional media. Approximately 94% of the phosphorus in P_aCSH was recycled into the biomass. This study successfully demonstrated the recycling the phosphorus recovered from wastewater for microalgal cultivation by aCSH.

Selection and characterization of microalgae with potential for nutrient removal from municipal wastewater and simultaneous lipid production.

Wastewater treatment, along with the simultaneous production of valuable chemical compounds, including lipids by microalgae is a challenging but attractive study. Towards this goal, the candidate microalgae were selected from culture collections or isolated from wastewater in this study. The initial screening test using microalgae revealed that various eukaryotic as well as prokaryotic microalgae showed steady growth in municipal wastewater samples. Among them, Tetraselmis sp. NKG400013 and Parachlorella kessleri NKG021201 from culture collections, and Chloroidium saccharophilum NKH13 from the wastewater sample exhibited high biomass productivity. Furthermore, P. kessleri NKG021201 and C. saccharophilum NKH13 showed high lipid productivity (56 ± 1 mg/L/day for NKG021201, 35 ± 10 mg/L/day for NKH13). During this cultivation, 99% of nitrogen and 82% of phosphorous compounds were removed from the wastewater sample by the strain NKG021201. Analysis of fatty acid compositions of P. kessleri NKG021201 and C. saccharophilum NKH13 revealed that lipids derived from these microalgae were suitable for the application of biodiesel fuels, indicating that these microalgae were promising for wastewater treatment and lipid production.

Characterization of a novel marine unicellular alga, Pseudoneochloris sp. strain NKY372003 as a high carbohydrate producer.

Production of biofuels and fine chemicals from biomass-derived carbohydrates through biorefinery attracts much attention because it is recognized as an environmentally friendly process. Microalgae can serve as promising carbohydrate producers for biorefinery rather than woody and crop biomass due to high biomass productivity, high CO2 fixation, and no competition with food production. However, microalgae with high carbohydrate productivity have not been well investigated despite intensive studies of microalgal lipid production. In this study, the carbohydrate production of Pseudoneochloris sp. strain NKY372003 isolated as a high carbohydrate producer, was investigated. Cultivation conditions with various combinations of nutrient contents and photon flux density were examined to maximize the biomass and carbohydrate productivities. At the optimal condition, the biomass and carbohydrate production of this strain reached 8.11 ± 0.37 g/L and 5.5 ± 0.2 g/L, respectively. As far as we know, this is the highest carbohydrate production by microalgae among ever reported. Cell staining with Lugol's solution visualized intracellular starch granules. Because algal starch can be converted to biofuels and building blocks of fine chemicals, Pseudoneochloris sp. NKY372003 will be a promising candidate for production of fermentable carbohydrates towards biofuels and fine chemicals production.

Advanced treatment of swine wastewater using an agent synthesized from amorphous silica and hydrated lime.

Advanced treatment using an agent synthesized from amorphous silica and hydrated lime (M-CSH-lime) was developed and applied to swine wastewater treatment. Biologically treated wastewater and M-CSH-lime (approximately 6 w/v% slurry) were fed continuously into a column-shaped reactor from its bottom. Accumulated M-CSH-lime gradually formed a bed layer. The influent permeated this layer and contacted the M-CSH-lime, and the treatment reaction progressed. Treated liquid overflowing from the top of the reactor was neutralized with CO2gas bubbling. The colour removal rate approximately exceeded 50% with M-CSH-lime addition rates of > 0.15 w/v%. The removal rate of PO(3⁻)(4) exceeded 80% with the addition of>0.03 w/v% of M-CSH-lime. The removal rates of coliform bacteria and Escherichia coli exceeded 99.9% with > 0.1 w/v%. Accumulated M-CSH-lime in the reactor was periodically withdrawn from the upper part of the bed layer. The content of citric-acid-soluble P2O5 in the recovered matter was>15% when the weight ratio of influent PO(3⁻)(4) -P to added M-CSH-lime was > 0.15. This content was comparable with commercial phosphorus fertilizer. The inhibitory effect of recovered M-CSH-lime on germination and growth of leafy vegetable komatsuna (Brassica rapa var. perviridis) was evaluated by an experiment using the Neubauer's pot. The recovered M-CSH-lime had no negative effect on germination and growth. These results suggest that advanced water treatment with M-CSH-lime was effective for simultaneous removal of colour, [Formula: see text] and coliform bacteria at an addition rate of 0.03-0.15 w/v%, and that the recovered M-CSH-lime would be suitable as phosphorus fertilizer.

Simultaneous removal of colour, phosphorus and disinfection from treated wastewater using an agent synthesized from amorphous silica and hydrated lime.

An agent synthesized from amorphous silica and hydrated lime (CSH-lime) was investigated for its ability to simultaneously remove the colour, phosphorus and disinfection from the effluents from wastewater treatment plants on swine farms. CSH-lime removed the colour and phosphate from the effluents, with the colour-removal effects especially high at pH 12, and phosphorous removal was more effective in strongly alkaline conditions (pH > 10). Colour decreased from 432 +/-111 (mean +/- SD) to 107 +/- 41 colour units and PO4(3-)P was reduced from 45 +/- 39 mg/L to undetectable levels at the CSH-lime dose of 2.0% w/v. Moreover, CSH-lime reduced the total organic carbon from 99.0 to 37.9 mg/L at the dose of 2.0% w/v and was effective at inactivating total heterotrophic and coliform bacteria. However, CSH-lime did not remove nitrogen compounds such as nitrite, nitrate and ammonium. Colour was also removed from dye solutions by CSH-lime, at the same dose.

Novel technique for phosphorus recovery from aqueous solutions using amorphous calcium silicate hydrates (A-CSHs).

A novel technique for phosphorus (P) recovery from aqueous solutions was developed using amorphous calcium silicate hydrates (A-CSHs). A-CSHs, which have a high Ca/Si molar ratio of 2.0 or greater, could be synthesized using unlimitedly available, inexpensive materials such as siliceous shale and calcium hydroxide. A-CSHs showed high performance for P recovery from an anaerobic sludge digestion liquor (ASDL) and the synthetic model liquor (s-ASDL) containing 89 mg PO4-P/L. After 20 min mixing, 1.5 g/L A-CSHs could remove approximately 69 and 73% PO4-P from ASDL and s-ASDL, respectively. By contrast, autoclaved lightweight concrete particles, which contained crystalline calcium silicate hydrates as a principal component, removed only 10 and 6% PO4-P from ASDL and s-ASDL, respectively, under the same experimental conditions. When A-CSHs were washed with deionized water to remove free Ca(OH)2, P removability was significantly improved (up to 82%) despite the reduction in the amount of Ca(2+) released. Unlike in the case of Ca(OH)2, no significant carbonate inhibition was observed with P removal by A-CSHs. Moreover, P removed by A-CSHs showed better settleability, filterability, and dewaterability than P precipitated with conventional CaCl2 and Ca(OH)2. The present study demonstrated that A-CSHs have great potential as a novel, beneficial material for P recovery and recycling.