Development of a new wastewater treatment process for resource recovery of carotenoids

A new wastewater treatment process that involves coagulation, ozonation, and microalgae cultivation has been developed. Here, two challenges are discussed. The first was minimizing phosphorus removal during coagulation in order to maximize algal production. The second was to optimize microalgae cultivation; algal species that grow rapidly and produce valuable products are ideal for selection. Haematococcus pluvialis, which produces the carotenoid astaxanthin, was used. Growth rate, nutrient removal ability, and astaxanthin production of H. pluvialis in coagulated wastewater were investigated. After coagulation with chitosan, the turbidity and suspended solids decreased by 89% ± 8.4 → 8% and 71 → 73% ± 16%, respectively. The nitrogen and phosphorus contents of the supernatant remained at 86% ± 6% and 69 → 67% ± 24%, respectively. These results indicate that coagulation with chitosan can remove turbidity and SS while preserving nutrients. H. pluvialis grew well in the supernatant of coagulated wastewater. The astaxanthin yield from coagulated wastewater in which microalgae were cultured was 3.26 mg/L, and total phosphorus and nitrogen contents decreased by 99.0% ± 1.4% → 99% + 1% and 90.3% ± 7.6% → 90% ± 8% (Days 31–35), respectively.</jats:p

Removal of Humic Substances by Repeated Mixing with PACl

Focusing on the improvement of removal efficiency of humic substances by coagulation, coagulation-flocculation processes were applied not only once but more than twice to the water being treated, and the effect of repeated coagulation was evaluated in jar-tests. With more than the critical dosage of PACl (15 mg/l), approximately 30% of color removal was attained in typical one-pass treatment, whilst maximum 65% removal was achieved by repeating the coagulation twice. Repeating coagulation enhances the coagulation process to achieve higher color removal efficiency, and can reduce the coagulant dosage.</jats:p

Phosphorus mass-quantity change in Lake Biwa

To understand the eutrophication phenomena in Lake Biwa, Japan, a research project for the water quality formation processes was executed. This paper presents phosphorus mass changes in water body in Lake Biwa from April 1995 to January 2000 and discusses the main factors of the change. Phosphorus mass ranged from 190 to 350 t, with an average of 260 t. DP mass in 1995, '97 and '98 showed seasonal change patterns, while non-periodical phenomena seemed to control the PP mass. Phosphorus mass was increased about 15 t in epilimnion from April to July while nitrogen showed a 50 t decrease. This disagreement suggests that some processes selectively accumulated phosphorus in epilimnion during this period. However, such an increase in phosphorus was not observed in 1996 and '99. Air temperature was lower and much snowfall was recorded in 1996 and '99, suggesting that coldness in winter season weakened the phosphorus accumulation process to depress the mass in epilimnion in summertime. Water temperature increase seemed to be delayed in proportion to total snowfall, but thermocline was formed independently of coldness. Hence, the idea was abandoned that the delay of thermocline formation encouraged the sedimentation process, and biological activities were considered to be the main factor controlling phosphorus mass in the epilimnion in Lake Biwa.</jats:p

Water quality characteristics of forest rivers around Lake Biwa

Forest river surveys were carried out at upper streams of several rivers in the Lake Biwa watershed to understand the water quality characteristics of the rivers, and to find out their relationships with forest features such as geographical, geological and vegetational data. The results showed: (1) Forests have some purification functions for nitrogen and organic matter, but become sources for most of ionic species. (2) Main mineral species in forest rivers are Ca2+, Mg2+ and Na+, HCO3–, CO32–, Cl–, SO42– and SiO2. (3) Loading from forests was 0.4–7 kg/km2/d for TN and 0.01–0.3 kg/km2/d for TP. (4) River quality reflects the properties of each forest, and is unique to the place, especially in ionic species such as Ca2+ and Cl–. (5) A cluster analysis successfully categorized ionic components into several groups.</jats:p