S. Chen, M. Rahman, R. H. Chabreck, B. F. Jenny, R. F. Malone 1
Two-stage lagoon systems are commonly used in the dairy industry for treatment of wastewater generated by the washing of feed-lots. Quite often, water quality from these lagoons does not meet the standards for effluent discharge. Therefore, further treatment is necessary before discharge is allowed. This paper presents the preliminary results of a demontration/research project that is using several types of aquatic plant systems as tertiary treatment units for improvement of lagoon effluent quality. This paper focuses on two of the systems in the project; a pond with black willow Salix niger and duckweed Spirodela sp., and a pond with water hyacinths Eichhornia crassipes. Hydraulic loading to the ponds varied from 0 to 107 m3/ha/day (0 to 11,520 gal/ac/day) except during rainy periods. Each of these systems was effective in the removal of total suspended solids (TSS), biological oxygen demand (BOD5), and fecal coliforms. Effluent from the lagoon system had a mean TSS of 253 mg/l and a mean BOD5 of 80.0 mg/l. Effluents from the tertiary treatment systems had a mean TSS of 57.0 mg/l (duckweed) and 37 mg/l (hyacinth), and a mean BOD5 of 19.0 mg/l (duckweed) and 17.2 mg/l (hyacinth). Fecal coliform reduction was approximately one order of magnitude from the lagoon effluent to the tertiary system effluent. However, effluents from the tertiary system had low dissolved oxygen and high ammonia concentration.
