The effect of anaerobic baffled reactor effluent on nitrogen and phosphorus leaching from four soils in a laboratory column experiment

Goitom Adhanom,Jeffrey Hughes,Alfred Odindo

doi:10.4314/wsa.v44i1.01

Abstract

Leaching of nitrogen and phosphorus from soil columns during application of anaerobic baffled reactor effluent was evaluated. The soils used were from Inanda (Ia), Cartref (Cf), and Sepane (Se) forms, and a silica sand (SS). Each was packed into duplicate columns (103 mm internal diameter; 200 mm length), four each for up-flow and down-flow leaching. Effluent was delivered continuously for 6, 8 and 35 days at high (32 mm·h-1), medium (16 mm·h-1), and low (2 mm·h-1) rates, respectively. At each flow rate, 9 pore volumes were collected. Leachates were analysed for pH, electrical conductivity (EC), nitrate and phosphate. Leachate pH from all soils was lower than the original effluent (6.4). Leachate EC varied between 0.5 and 0.9 dS·m-1 compared to the effluent EC of 0.84 dS· m-1. At high flow rate, the amount of nitrogen leached was similar from all soils. At low and medium rates, more nitrogen was leached from the coarser-textured SS and Cf than the finer-textured Ia and Se, at both flow directions. Flow direction had a greater effect on nitrogen leaching from finer- than coarser-textured soils. Phosphorus concentrations were higher than the original effluent at medium and high flow rates indicating that the soils were a source of phosphorus. At low flow rate, phosphorus concentrations were much lower than the original effluent, indicating soil retention. Phosphorus leaching was greater from coarser- than finer-textured soils in the up-flow columns, but the opposite occurred in the down-flow columns.

Highlights

Urban municipalities in South Africa, in common with many worldwide, are faced with increasing challenges of providing housing and related infrastructure
It was found that the anaerobic baffled reactor (ABR) effluent resulted in higher electrical conductivity (EC) values in the first pore volumes (PVs) of leachate compared to the soil EC (Table 1), indicating a low soluble salt (EC) attenuation by the soils
This was further supported by the calculation that 59 to 95% of the applied effluent salts were leached through the soil columns at each PV (Fig. 3)

Summary

Introduction

Urban municipalities in South Africa, in common with many worldwide, are faced with increasing challenges of providing housing and related infrastructure. One of these challenges is that of providing adequate sanitation facilities and safe disposal of the wastes produced. Land application of wastewater provides the opportunity of using the water for irrigation while utilising the chemical, physical, and biological properties of the soil/plant system to assimilate the waste components without adversely affecting soil quality or causing contaminants to be released into water or the atmosphere (Loehr, 1984; Chahal et al, 2011). Application of wastewater to land can affect both soil and water quality. Wastewaters used for irrigation could influence the physical, chemical and biological properties of the soils (Feigin et al, 1991; Mathan, 1994; Schipper et al, 1996) which, in turn, play an important role in the transformation of nutrients present in the applied wastewater

Methods

Results

Conclusion