Page 204 - AJWEP-22-6

Asian Journal of Water, Environment and Pollution. Vol. 22, No. 6 (2025), pp. 198-209.
doi: 10.36922/AJWEP025320249

ORIGINAL RESEARCH ARTICLE

Stage-wise performance evaluation of the Kalobe waste
stabilization ponds in Mbeya, Tanzania: Efficiency in

organic load and nutrient removal

Eline Gerson 1,2 , Gislar E. Kifanyi , Omary R. Shegwando 1,2 ,
1
and Fredrick Ojija *
3
1 Department of Civil Engineering, College of Engineering and Technology, Mbeya University of
Science and Technology, Mbeya, Tanzania
2 Department of Technical, Mbeya Water Supply and Sanitation Authority, Mbeya, Tanzania
3 Department of Earth Sciences, College of Science and Technical Education, Mbeya University of
Science and Technology, Mbeya, Tanzania
*Corresponding author: Fredrick Ojija (fredrick.ojija@must.ac.tz)

Received: August 9, 2025; Revised: August 29, 2025; Accepted: September 3, 2025; Published online: October 3, 2025

Abstract: Globally, waste stabilization ponds (WSPs) in warm climates have demonstrated high treatment
efficiencies for organic matter and suspended solids. This study evaluates the stage-wise performance and overall
treatment efficiency of the Kalobe WSPs in Mbeya city, Tanzania, which treat approximately 15,000–18,000 m /day
3
of mixed domestic and industrial wastewater, compared with a design capacity of 28,800 m /day. The system
3
comprises anaerobic, facultative, and maturation ponds operating in parallel. Field sampling and laboratory
analysis were conducted to determine pollutant concentrations across each treatment stage, focusing on key
parameters including biochemical oxygen demand (BOD), 5-day, chemical oxygen demand (COD), total suspended
solids (TSSs), ammonia, nitrite, and total dissolved solids (TDS). Results revealed that while the WSP system
demonstrated high removal efficiencies for organic and solid pollutants, achieving reductions of 58.1% for BOD,
87.3% for COD, and 87.2% for TSS, its performance in nutrient and dissolved solids removal remained limited.
Ammonia was moderately reduced (80.5%), whereas nitrite and TDS exhibited low removal efficiencies of 17.4%
and 13.7%, respectively. The final effluent BOD (39 mg/L) and COD (78 mg/L) exceeded Tanzania’s national
discharge standards, indicating partial non-compliance. The study also found that flow variations, particularly from
industrial contributors such as Pepsi and Tanzania Breweries Limited, introduced intermittent hydraulic shocks,
which may impair treatment consistency. The findings highlight the need for system upgrades, enhanced industrial
pre-treatment enforcement, and the integration of post-treatment units to improve nutrient polishing. Overall, while
Kalobe WSPs remain a cost-effective solution, strategic interventions are necessary to ensure sustained regulatory
compliance and environmental protection.

Keywords: Waste stabilization ponds; Treatment efficiency; Organic load reduction; Nutrient removal; Anaerobic
ponds; Facultative ponds; Maturation ponds

Volume 22 Issue 6 (2025) 198 doi: 10.36922/AJWEP025320249