Diagnosis of Natural-Based Wastewater Treatment Plant Using Induced Polarization Method

Greywater treatment using natural-based solutions has been considered a sustainable solution for domestic wastewater treatment in small communities for around two decades. Natural-based solutions usually use a vegetated porous medium for water flow, either vertically or horizontally, but clogging is a primary issue due to non-regular flow velocity distribution and preferential flow pathways. The studied site treats domestic wastewater from 1,000 people with a mean flow rate of 150 m³/day, using septic tanks and gravel-based horizontal subsurface flow units, followed by maturation ponds and refining filters. After 10 years of operation, signs of clogging led to partial gravel renewal in one of the treatment gravel ponds.

The study aimed to use time-domain-induced polarization geophysical techniques to map and quantify clogging levels without interfering with the water regeneration procedure. Ten resistivity and induced polarization cross-sections were acquired before and after the gravel replacement procedure.

From this tomography and the defined relationship between the normalized chargeability and the weight amount of clogging, we are able to image in 3D the distribution of clogging and where it is concentrated in the filter before and after the improvement tasks carried out by the facility management team.