Series Of Stabilization Ponds Research Articles

Performance of a system combining aerated lagoons and waste stabilization ponds in a temperate climate

AbstractThe Bertrix wastewater treatment plant was designed and built for experimental purposes, especially for comparing aerated lagoons and stabilization ponds in a temperate climate. This plant was designed for a capacity of 7500 inhab. eq, and aerated lagoons were dimensioned to eliminate 50% of the organic load. The remaining load has to be degraded in the series of stabilization ponds. In this paper we shall present the plant in more detail and the results of a 3-year study, i.e., 79 rounds of samples for each of the five ponds under study, placing emphasis on the performances of aerated lagoons and stabilization ponds. Principal components analysis (of inflow and outflow) of aerated lagoons and stabilization ponds will be presented and commented on. The most important factors are the hydraulic loading and the concentrations. Seasonal variations appear only in the basins' temperatures. The fates of nitrogen compounds are quite different from those of organic compounds, confirming that a high efficiency of nitrogen removal is difficult to achieve, especially for short residence times (less than eight days). A few other conclusions of our study are given below: The ponds' hydrodynamics has been studied and a mathematical model is now available If there is no stratification in the ponds, a thermal model can be proposed where the mean absolute difference is 0.7°C±0.2. In the system under study, the contribution of algal biomass to the system is very small.

Stabilization ponds with recirculation

The first facultative pond in a series of stabilization ponds, or else the first part of a large pond, is sensitive to organic overloading creating anoxic or anaerobic conditions at the pond's surface, resulting in malodors and nuisances. Such adverse characteristics are usually manifested seasonally when climatic conditions change to lower temperatures and/or reduced solar irradiance. The design organic loadings on such ponds are therefore determined by the critical season and they are lowered accordingly. Introducing recirculation of effluent from a later pond in the series (usually from the second or third pond) back to the inlet of the first one, at a ratio of 1.0 - 2.5 (recirculated effluent) to 1 (raw sewage influent), can be most advantageous, as follows: (1) organic loadings on the first facultative pond in the series can reach 400-600 kg BOD5 per hectare per day (khd) during summer time and 300-400 khd as a yearly average, compared with a yearly average of 60-140 khd on ordinary facultative ponds, while still maintaining odor-free facultative conditions; (2) reseeding the first pond with active adapted algal biomass; (3) mixing the influent (which is often septic) with oxygen-rich recirculated effluent, thus enhancing the biological process in the first pond and suppressing septic odors, and (4) the increased inlet flow (by combining influent flow with the recirculated effluent) increases the area of solids (sludge) settling in the first pond. Altogether, the recirculation is manifested by reduced land requirements, better stability in pond operation, improved pond's performance and reduction or elimination of malodors and nuisances. Step feeding of the ponds further accentuates the effect of recirculation. Obviously, recirculation requires pumping (low head), energy, piping and connection to a power supply. The cost of operation and maintenance amount to US $0.01-0.02 per cubic metre of treated wastes. The advantages of recirculation nevertheless significantly outweigh the added costs. The paper describes the experience and data which have been gathered during the operation of 120 hectares of ponds with recirculation in the Dan Region (Greater Tel-Aviv) over a period of almost 20 years.

Stabilization ponds with recirculation

The first facultative pond in a series of stabilization ponds, or else the first part of a large pond, is sensitive to organic overloading creating anoxic or anaerobic conditions at the pond's surface, resulting in malodors and nuisances. Such adverse characteristics are usually manifested seasonally when climatic conditions change to lower temperatures and/or reduced solar irradiance. The design organic loadings on such ponds are therefore determined by the critical season and they are lowered accordingly. Introducing recirculation of effluent from a later pond in the series (usually from the second or third pond) back to the inlet of the first one, at a ratio of 1.0 – 2.5 (recirculated effluent) to 1 (raw sewage influent), can be most advantageous, as follows: (1) organic loadings on the first facultative pond in the series can reach 400–600 kg BOD5 per hectare per day (khd) during summer time and 300–400 khd as a yearly average, compared with a yearly average of 60–140 khd on ordinary facultative ponds, while still maintaining odor-free facultative conditions; (2) reseeding the first pond with active adapted algal biomass; (3) mixing the influent (which is often septic) with oxygen-rich recirculated effluent, thus enhancing the biological process in the first pond and suppressing septic odors, and (4) the increased inlet flow (by combining influent flow with the recirculated effluent) increases the area of solids (sludge) settling in the first pond. Altogether, the recirculation is manifested by reduced land requirements, better stability in pond operation, improved pond's performance and reduction or elimination of malodors and nuisances. Step feeding of the ponds further accentuates the effect of recirculation. Obviously, recirculation requires pumping (low head), energy, piping and connection to a power supply. The cost of operation and maintenance amount to US $0.01–0.02 per cubic metre of treated wastes. The advantages of recirculation nevertheless significantly outweigh the added costs. The paper describes the experience and data which have been gathered during the operation of 120 hectares of ponds with recirculation in the Dan Region (Greater Tel-Aviv) over a period of almost 20 years.