Algae ͑green, blue-green, and diatom͒ grown in inorganic media produced particulate and dissolved organic carbon ͑DOC͒. DOC produced by a green-alga contains 25% hydrophobic acids. DOC from all algae had specific ultraviolet absorbance values less than 2.0 m −1 ͑mg/ L͒ −1. Algae-produced DOC was biologically labile; greater than 60% degraded in bioreactors within 5 days. The biodegradable material likely included carbohydrates, amino acids, and amino sugars, which were present in hydrophobic acid isolates. Chlorination of algal DOC formed disinfection by-products; DOC from the green alga, Scenedesmus quadricauda, produced chloroform ͓0.53 micromole per mg carbon ͑mol/ mg C͔͒, dichloroacetic acid ͑0.27 mol/ mg C͒, and trichloroacetic acid ͑0.14 mol/ mg C͒. This work complements other studies, which focused on algal total organic carbon ͑DOC and cellular material͒, and clearly demonstrates the importance of identifying algae-derived sources of DOC in water supplies and removing such DOC in water treatment plants prior to chlorination.

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Two seasonal sampling campaigns of raw and finished waters from 28 water treatment plants were conducted to investigate the occurrence and removal of dissolved organic nitrogen (DON). A new dialysis pretreatment technique was applied for accurate DON determination. The average DON concentration was 0.186 mg/L nitrogen (N) in raw waters and 0.148 mg/L N in finished waters. On average, total dissolved nitrogen in the raw waters consist of 10% DON and 90% dissolved inorganic nitrogen. The dissolved organic carbon (DOC)‐to‐DON ratio of raw waters averaged 18 mg DOC to 1 mg DON. DON removal during water treatment closely mirrored that of DOC removal. The molecular weight distribution of DON roughly parallels that of DOC, and higher‐molecular‐weight fractions (> 10,000 D) of both DON and DOC were preferentially removed across the full‐scale water treatment plants.

Microalgae can be cultured in photobioreactors to sequester carbon dioxide and produce potentially valuable biomaterials. The goal of the present study was to identify and utilize microalgal strains that are capable of tolerating up to 20% CO2 (gas phase) concentrations under variable light or flue-gas blend conditions and reactor configurations to produce biomass. Scenedesmus sp. and Chlorella sp., both cultured from a Sonoran desert mineral spring, grew well and tolerated exposure to a gas mixture containing up to 20% CO2 applied continuously in batch reactors to the culture. Experiments were conducted with simulated coal-powered acidic flue gases containing SOx/NOx at concentrations of 200 to 350 ppmV. Microalgae did not grow well without pH control, and high levels (>250 mM) of nitrite or sulphite in the liquid media inhibited algal growth. Pseudo steady-state experiments were also conducted using helical tubular and flat-plate photobioreactors with continuous flow (water and gas) and with artificial or natural sunlight. With a 2 d hydraulic residence time (HRT), the helical tubular photobioreactor produced 0.50 +/- 0.11 g C d(-1) (0.056 +/- 0.012 g C L(-1) d(-1)) dry-weight cell mass during continuous fluorescent-lamp irradiance and 0.048 +/- 0.018 g C L(-1) d(-1) during 12 h light/darkness cycling. The flat-plate photobioreactor (2 d HRT) produced 0.42 +/- 0.28 g C L(-1) d(-1) with artificial lighting and with natural sunlight; a 4 d HRT produced 0.14 +/- 0.02 g C L(-1) d(-1). Reactor modelling indicated that a threshold of reactor size (i.e., HRT) an d reactor depth (path-length of light) exists based upon the optical density of the cells in the water column and their growth rates.