Seasonal distribution of cadmium among components of sewage treatment ponds: an eco-tech for heavy metal remediation

The study was designed to quantify cadmium accumulation in different components of sewage treatment ponds during different seasons and to assess risk for human consumption perspective. The study estimated cadmium concentration in water, sludge, Eichhornia, plankton and tilapia fish from anaerobic, facultative, maturation-1 and -4 ponds during pre-monsoon, monsoon and post-monsoon periods. It resulted that cadmium accumulated among different components of anaerobic, facultative, maturation-1 and -4 ponds ranging 0–18, 0–10, 0–7 and 0–15.4 ppb, respectively. During monsoon, highest accumulation was observed in tilapia in both facultative and maturation ponds, but during post-monsoon, plankton community showed highest value in all. The highest bio-magnification of cadmium was recorded during monsoon with varying degrees (facultative pond: 4.39, maturation pond-1: 3.03 and maturation pond-4: 7.08). Cadmium concentration in tilapia lied within WHO’s safe level and may be recommended for human consumption. The concentration of cadmium was estimated by Flame Atomic Absorption Spectrophotometer. The above findings occurred due to chelation, adsorption and sedimentation, absorption and bio-accumulation, ionization, leaching through sediment and rainfall. Water pH (6.7–8.8), dissolved oxygen (0–17 mg L^?1), total solids (251–650 mg L^?1), iron (Fe²⁺) concentration (0.61–4.87 mg L^?1) and sedimentation rate (278.9–2,409.6 g day^?1 m^?3) were conducive for the distribution of cadmium into different ecosystem components of treatment ponds. These ponds reclaimed 28.57–61.11 % of sewage-cadmium and may be promoted as a low-cost eco-tech for sewage treatment.