Nutrient removal in wastewater treatment high rate algal ponds with carbon dioxide addition

摘要

The influence of CO2 addition to high rate algal ponds (HRAPs) on nitrogen removal wasninvestigated using two pilot-scale HRAPs operated with different hydraulic retention timesn(HRT: 4 and 8 days), and was compared to the nitrogen removal by the 8-day HRT pond beforenCO2 addition was installed. Nitrogen balances were calculated by partitioning total nitrogen intonorganic and inorganic nitrogen (NH4nþ-N and NO3nu0002-N), and by separation of the organic nitrogenninto particulate (PON) and dissolved organic nitrogen (DON). PON was further divided into algalnorganic nitrogen (AON) and bacteria organic nitrogen (BON) to investigate nitrogen mass flow innthe HRAPs. This research shows that the proportion of algae in the algal/bacterial biomass innthe longer 8-day HRT HRAP8d (55.6%) was appreciably lower than that in the shorter 4-daynHRT HRAP4d (80.5%) when CO2 was added to control the maximum pH to o8.0 during thensummer. Higher bacterial biomass in the longer 8-day HRT HRAP corresponded with highernnitrification rates, indicating that the longer 8-day HRT in the summer was detrimental for twonreasons: lower algal productivity and increased nitrogen loss through nitrification/denitrification.nOverall nitrogen removal of B60% in the HRAPs with CO2 addition was mainly achieved by algalnassimilation followed by sedimentation in the settling unit.