Performance comparison between two equal stabilization ponds operating with and without sludge layer

Abstract

Stabilization ponds are a highly appropriate system for treating sewage in small to medium size communities. However, sludge accumulation at the pond bottom occurs with the passage of time, reducing the net pond volume, which, in principle, could affect its performance. The objective of this paper is to compare the behaviour of two equal ponds in parallel treating the same flow of municipal wastewater from an upflow anaerobic sludge blanket reactor in Brazil. Each pond treated a population equivalent of around 125 inhabitants. One pond had approximately 40% of its net volume occupied by sludge after 11 years of operation, while the other pond had previously undergone complete desludging. The study covers the removal of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), nitrogen fractions and coliforms. Owing to the presence of a sludge layer, the theoretical hydraulic retention time (HRT) was lower in the pond without sludge. For BOD, COD, SS and Escherichia coli there were no significant differences (Wilcoxon matched-pairs test) between both ponds. The pond without sludge had significantly better removal efficiencies in terms of total Kjeldahl nitrogen and ammonia-N. The sludge layer probably allowed the occurrence of removal mechanisms that compensated for the reduction caused in the HRT.

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

“…The previous setup had been in operation for over 10 years and was well documented in an overall performance evaluation paper by Dias et al (2014). Other researches have been conducted on this previous system documenting different evaluations on specific subjects, and they can be found, for instance, in Araújo et al (2010), Godinho et al (2011 and Rodrigues et al (2015). Flow-through or continuous flow ponds are used here, since they are the most common type of pond units, compared with the alternative of batch-fed ponds.…”

“…The first pond accumulated a large amount of sludge over the previous 11 years (Possmoser-Nascimento et al 2014) and was investigated regarding ammonia and nitrogen fractions removal (Rodrigues et al 2015).…”

“…Araújo et al (2010) studied the same ponds (previous set up) and verified the presence of annamox bacteria in the sludge. Rodrigues et al (2015) analysed nitrogen removal in Ponds 1 and 2 when they operated in parallel, for six months, immediately before upgrading and insertion of baffles: Pond 1 with accumulated sludge on the bottom, while Pond 2 had been recently desludged. Even with sludge occupying 40% of its useful volume and thus reducing HRT, Pond 1 was able to remove total nitrogen similarly to the pond without sludge.…”

The Role of Environmental Variables in Waste Stabilization Ponds' Morphodynamics

“…Sludge accumulation patterns impact the pond hydraulics directly as a result of reduction in the effective pond volume and modified pond bottom surface (Alvarado et al, 2012a;Murphy, 2012;Rodrigues et al, 2015;Coggins et al, 2017). Although some research suggest that sludge accumulations result into longer HRT (Alvarado et al, 2012a) and do not cause any significant reduction in organic pollutants removal (Passos et al, 2014a), nutrients removal especially nitrogen seem to be significantly affected by the presence of sludge (Passos et al, 2014a).…”