Optimisation of domestic wastewater treatment for Matagalpa, Nicaragua

LeAF assisted Waterboard De Dommel in their plans to optimise the current centralised domestic wastewater treatment plant (WWTP) of Matagalpa, Nicaragua, as well as to propose wastewater management options for newly established ‘satellite’ settlements.

A  thorough design analysis was made based on the provided data. In addition, an alternative treatment plant using UASB technology was proposed, including a first rough idea of the required reactor size. With respect to the satellite settlements, technological concepts for decentralised  wastewater management were explored.

The city of Matagalpa has a centralised WWTP serving approximately 50% of inhabitants connected to the sewerage. Treatment takes place in stabilisation ponds, preceded by pre-treatment using a coarse screen and a degritter. The configuration of the stabilisation ponds is a ‘classical’ one: two parallel anaerobic ponds, followed by one facultative pond. Post-treatment takes place in one maturation pond. The treated effluent is discharged into the Rio Grande river via a cascade. The performance of the WWTP is far from optimal. As the pre-treatment step is not well designed and operated, debris and sand are not prevented from entering the stabilisation ponds. In addition the ponds have not been regularly maintained, leading to accumulation of sludge, decrease of operating volume and short circuiting of the wastewater. Consequently, the residence time in the system us shorter than desired and solids are flushed out, leading to decreasing effluent quality.

Characteristic for the region of Matagalpa is a spontaneous development of new, small settlements that are located in the peri-urban area, usually too far away to be easily connected to the sewer. Semi-decentralised solutions involving a treatment system for each settlement may provide the best solution for wastewater management for those cases.

The described activities are part of the project ‘Futuragua - Capacity development of Nicaraguan partners at Matagalpa Municipality and ENACAL Drinking water Utility’ that is executed by Waterboard De Dommel in the context of  the twinning Tilburg-Matagalpa.

For more information on the LeAF part of these activities, please contact Iemke Bisschops or Katarzyna Kujawa-Roeleveld.