Underground Sewer Monitoring System: Nanning Case

Underground sewer monitoring system for a 65 km Nanning sewer network improved corrosion resistance, cut maintenance costs, and raised valid data from 75% to 98%.

Project Background

A wastewater sewer network in Nanning covers approximately 65 km and serves more than 200,000 people.

Because of the subtropical climate, frequent rainfall and high groundwater levels, underground manholes operate under high humidity, elevated hydrogen sulfide (H₂S) and highly corrosive conditions.

These conditions created a direct reliability problem for water quality monitoring equipment. Conventional instruments had an average service life of only six months, while annual maintenance costs exceeded RMB 200,000.

Corrosion also caused sensor drift and communication failures, reducing the valid data rate to only 75%. According to the project record, an equipment failure once resulted in missing critical monitoring data during an illegal wastewater discharge event.

Maintenance was equally difficult. Equipment required a full inspection approximately every two months, taking around three hours per monitoring point, while personnel working around underground manholes also faced potential H₂S exposure risks. OSHA notes that hydrogen sulfide can accumulate in sewers and manholes and create serious confined-space hazards.

Corrosion-Resistant Monitoring Solution

The project therefore focused on three requirements: corrosion resistance, reliable data and lower maintenance.

Corrosion protection. Core system components used a 316L stainless steel housing with a PTFE anti-corrosion coating, while sensor probes used acid- and alkali-resistant materials. The equipment design life was extended to three years for the high-H₂S and high-humidity underground environment.

Stable data transmission. An anti-interference wireless transmission system was used to reduce communication failures in the underground environment. The project increased valid monitoring data to above 98%. The system also incorporated a battery with approximately six months of endurance and support for auxiliary solar power.

Remote maintenance. Automatic calibration, fault self-diagnostics and maintenance warnings reduced the need for frequent site inspections. Under normal operation, operators only needed to perform a remote data check once per month.

For similar projects requiring several parameters at one monitoring point, see APURE’s Multiparameter Water Quality Monitoring solutions.

Project Results

Indicator	Before	Project Result
Average equipment service life	About 6 months	Designed for up to 3 years
Valid monitoring data	75%	98%
Maintenance time	3 h/point	30 min/point
Labor cost	Baseline	Reduced by 70%
Equipment replacement cost	Baseline	Reduced by 80%
Equipment condition after 18 months	—	100% equipment integrity

After 18 months of operation, the project reported 100% equipment integrity, with no equipment damage attributed to corrosion.

Remote maintenance reduced single-point service time from approximately 3 hours to 30 minutes, while labor cost decreased by 70%. Equipment replacement cost was reduced by 80% compared with the previous monitoring arrangement.

More importantly, the valid data rate increased from 75% to 98%. During the reported operating period, the system detected six abnormal events, including illegal wastewater discharge and sewer leakage.

Why Corrosion Resistance Matters for Sewer Monitoring?

For underground sewer monitoring, measurement range alone does not determine whether a system will work reliably.

If H₂S, moisture and corrosion cause frequent sensor drift, communication failures or equipment replacement, the monitoring network can lose data exactly when abnormal wastewater events occur.

The Nanning project shows that combining corrosion-resistant materials, reliable wireless transmission and remote diagnostics can improve both data availability and operating cost in difficult underground environments.