High organic loading rate and waste stabilization pond's operation efficiency: a case study

摘要

Liquid waste management is an important component of sanitation activities. Waste stabilization pond system is very low cost, easy for maintenance and the stabilized water outflowing from the system can be used for irrigation purposes in agriculture, horticulture, etc. The affect of high organic loading rate and occurrence reasons of purple sulfur bacteria (PSB) in waste stabilization ponds were investigated. Chemical parameters which affect on PSB growth like COD, and hydrogen sulfide (H_2S) were observed monthly. The mixed culture populations of PSB were considered and determined by spectro-photometric method. The cell suspension was whitish pink when elemental sulfur globules occurred inside the cells, and turned purplish red once the globules were consumed. The measurement of flow was carried out by means of a Partial flume in which located at the inlet channel. Measurement of flow was done simultaneously with wastewater sampling. The measured average of COD concentration of raw wastewater with around 1520.33 mg/l was much higher than the expected design concentration of 550 mg/1, respectively, for COD. Thus, the raw wastewater in Hoveizeh can be classified as a high strength in terms of COD. Results showed that the PSB dominated in two periods, which the first was in midsummer (in primary facultative pond) and the second was in midwinter (in tertiary facultative pond). This condition was occurred by high organic loading rate (OLR) and high concentration of H_2S which were caused overcoming of the PSB over algae. Results showed that the OLR was the main affecting parameters in the overcoming of PSB. It could be suggested that by upgrading the capacity of the Hoveizeh facility (constructing parallel ponds), the problem caused by the purple sulfur bacteria could be dominantly reduced.