Performance of an Experimental Wastewater Treatment High‐Rate Algal Pond in Subarctic Climate

• Published in: Water Environment Research
• Main Authors: Grönlund, Erik, Hanæus, Jörgen, Johansson, Erica, Falk, Stefan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2010
• Subjects: Subarctic
• Online Access: http://dx.doi.org/10.2175/106143009x12487095236478; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2175%2F106143009X12487095236478; https://onlinelibrary.wiley.com/doi/pdf/10.2175/106143009X12487095236478

A pilot‐scale experimental high‐rate algal pond (HRAP) was investigated in the subarctic mid‐Sweden region, at latitude 63°N. During autumn 2002, conditions included temperatures below 10°C and photosynthetic active radiation below 200 µE/m 2 ·s. Biochemical oxygen demand was reduced by approximately 90% (approximately 40 g/m 3 ), chemical oxygen demand by 65% (approximately 80 g/m 3 ), total phosphorus by 20% (approximately 1 g/m 3 ), and total nitrogen by 46% (approximately 15 g/m 3 ), at a retention time of approximately 2.5 days. During autumn 2003, the performance of the HRAP appeared better with a more dense microalgae culture; however, as a result of poor settling of the microalgae, the reduction was considerably lower. A major difference between the years was the microalgae composition. In 2002, the large green algae Coelastrum dominated with Chlamydomonas , Scenedesmus , Lagerheimia , and the Cryptophyte Rhodomonas . In 2003, there was a total dominance of the very small green algae Chlorella , known to be difficult to settle. In batch growth experiments during spring 2002, doubling times of 4 to 6 days were achieved. The period of temperatures above 10°C and an insolation of more than approximately 270 uE/m 2 ·s (125 Langleys), which is well‐documented as appropriate for HRAP function ( Oswald, 1988a , 1988c ), were measured to last for 4 to 4.5 months from early May to late September. However, the growth and treatment performance experiments indicated that a longer season may be possible—6.5 to 7 months, at best—from early April to late October.