Occurrence dynamics of nitrogen compounds in faecal sludge stabilisation ponds in the Tamale Metropolis, Ghana

Abstract

Faecal sludge, with richness in soil nutrients represents an important resource for enhancing soil productivity. In this study, the occurrence dynamics of nitrogen compounds NH3, NO2- and NO3- in engineered waste stabilisation ponds in the Tamale metropolis was monitored for 5 months in the dry season. Four treatment ponds were divided into three units: Influent point, midpoint and effluent point for sampling purposes. Faecal sludge sampling was simultaneously carried out for each of the ponds at marked points and approximate depth of 30 to 50 cm using 500 ml sample collection bottles. Using the Nessler method and Powder Pillows NH3, NO3- and NO2- levels were determined through direct reading with a DR 2800 Spectrophotometer. Mean concentrations of NH3, NO3-, and NO2- were determined to be 42.65, 57.99 and 0.15 mg/l, respectively. The anaerobic pond on average, recorded the maximum concentration levels of all three compounds. The primary facultative pond recorded the average minimum concentration of NO2- while the maturation pond recorded the minimum for both NH3 and NO3. Variation in concentration of nitrogen compounds was statistically highly insignificant by ANOVA at 5% significance level, except NH3. Average NH3 concentrations in stabilisation ponds were observed to be higher than the allowable limit of EPA Ghana for effluent discharge or reuse for agriculture while NO3- was lower aside concentration in the anaerobic pond. The effluent should further be treated to reduce NH3 concentration using different treatment options such as the filter beds or constructed wetland prior to reuse for agriculture. Key words: Faecal sludge, stabilisation pond, nitrogen compounds, nitrification, denitrification.