Upgrading and evaluation of a simple pond system for small communities with simple interventions to reduce land requirements and increase performance

Abstract

The study covers different investigations related to the upgrading of a post-treatment system for the effluent from a upflow anaerobic sludge blanket reactor. The original post-treatment scheme comprised three ponds in series and a small coarse rock filter inserted in the last pond. Upgrading involved reducing the pond depths, applying baffles in the second pond and converting all of the third pond into a rock filter (three decreasing grain sizes). The system was conceived for 250 population equivalents, occupied an area of only 1.5 m2/inhabitant and aimed at very good removals of all major wastewater constituents. Overall final effluent concentrations for Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) were very good, and lower than those from the previous treatment line. Hydraulic flow patterns in both ponds showed daily thermal stratification and destratification periods. The conversion of the third pond into a rock filter increased the removal capacity of TSS (algae), but could potentially result in clogging, a phenomenon that was evaluated by a geophysical method called Georadar. The influence of accumulated sludge on treatment performance was tested before starting the operation of the upgraded system by operating the two ponds in parallel (one with sludge accumulated after 11 years of operation and the other without sludge). In this test, ammonia removal was virtually the same in both ponds.

Relationships between abiotic and biotic variables in a maturation pond and their influence on E. coli removal

“…The high values of DO are in accordance with Dias et al (2017a), and are probably a result of solar radiation exposure with the fewer clouds during the warmer season. In the southeastern region of Brazil, where the study was performed, the rainy season is essentially in spring and summer, when higher insolation is also detected (Figure 3(a)), resulting in greater growth rates of the autotrophic community and consequently higher photosynthesis rates and DO concentration in the water.…”

“…The experiments were conducted in the second maturation pond (44 cm depth) in a series of an upflow anaerobic sludge blanket (UASB) reactor, two maturation ponds and a rock filter. The treatment line had recently undergone interventions to decrease land requirements and increase overall efficiency, as described by Dias et al (2017a). The intervention in the second maturation pond resulted in lowered hydraulic retention time of 1.8 days and a surface organic loading rate (median and mean) of 147 and 161 kgBOD•ha À1 •d À1 .…”

“…Maturation ponds following a facultative or anaerobic pond can act as a polishing phase of the effluent by removing pathogenic organisms through the abiotic and biotic factors previously described. To improve final effluent quality in order to reuse it for other practices (e.g., irrigation), it is essential to understand the multitude of synergetic inactivation and decomposition mechanisms, which are complex and still considered enigmatic due to the range of transformations that organic matter and other constituents undergo (Dias et al 2017a).…”