Treatment Paths and Online Monitoring System Selection for Domestic Sewage and Domestic Wastewater

I. An Indispensable Conceptual Analysis in Engineering Design

For system integrators, IoT solution providers, and project contractors undertaking domestic drainage projects for residential communities, commercial complexes, schools, hospitals, or industrial parks, the first technical judgment is: whether the drainage source is domestic sewage or domestic wastewater.

This judgment directly determines the following engineering decisions:

• Whether the pipeline system adopts combined or separate sewerage

• Selection and range setting of online water quality monitoring instruments

• Whether a septic tank or pre-treatment facility is required

• Water source selection and treatment process for the water reuse system

However, many projects have vague definitions of "sewage" and "wastewater" in the early design stage, leading to unreasonable monitoring point settings, equipment selection deviations, and failure to pass acceptance inspections. From the perspective of project delivery, this article systematically sorts out the essential differences between the two and provides actionable monitoring system configuration recommendations.

II. Core Definitions: The Essential Difference Between Domestic Sewage and Domestic Wastewater

2.1 Source Differences Determine Pollutant Load

From the perspective of drainage source, the boundaries between the two are clear:

Core conclusion: Domestic sewage is toilet drainage, heavily polluted, with high treatment cost; domestic wastewater is washing drainage, lightly polluted, with high reuse value.

2.2 Engineering Differences in Treatment Paths

In actual projects, the treatment paths of the two types of water are distinctly different:

• Domestic sewage: Must be treated by a septic tank or integrated sewage treatment facility (such as A²O, MBR processes) before being discharged into the municipal sewage network or meeting discharge standards. If reuse is considered, the cost is high, and it is usually not the first choice for water reuse source.

• Domestic wastewater: Relatively clean; after simple physical treatment (such as screens, equalization tanks, coagulation sedimentation) or mild biochemical treatment, it can be used for non-potable purposes such as toilet flushing, green irrigation, road washing. It is the main water source for water reuse systems.

Engineering tip: When designing a water reuse system, prioritize using wastewater (hand, shower, laundry) as raw water rather than sewage. This judgment directly affects system scale, investment cost, and operation/maintenance difficulty.

III. Combined and Separate Sewerage: Two Paths in Water Supply and Drainage Design

3.1 Definitions of the Two Systems

• Combined Sewerage: Domestic sewage and domestic wastewater are discharged from the building through the same vertical pipe, converging into the same pipeline network system.

• Separate Sewerage: Domestic sewage and domestic wastewater are provided with independent drainage pipeline systems until they enter different treatment or collection points.

3.2 Respective Applicable Scenarios and Monitoring Points

Key advice: In new projects, if there are plans for water reuse or local government requirements for separate discharge of rainwater, sewage, and wastewater, a separate sewerage design must be adopted. This not only facilitates compliance management but also provides clear separate monitoring conditions for future deployment of online water quality monitoring systems.

IV. Engineering Difficulties in Domestic Sewage Treatment and Monitoring Responses

Based on actual project experience, domestic sewage treatment has the following significant difficulties in engineering implementation:

4.1 Seasonal Fluctuations in Water Quality and Quantity

• Difficulty: Holidays, summer/winter breaks, rainy periods cause drastic fluctuations in sewage flow and pollutant concentration. For example, in tourist city hotels, COD can increase by more than 50% during peak season.

• Monitoring response: Configure online COD and ammonia nitrogen analyzers with auto-ranging or wide dynamic range, and add flow meters to achieve dynamic statistics of pollution load.

4.2 Large Differences in Drainage from Different Water Facilities

• Difficulty: Within the same building, kitchen wastewater has high oil and grease, laundry wastewater has high phosphorus, shower wastewater has high surfactants. After mixing, the water quality is complex.

• Monitoring response: In separate systems, it is recommended to set node monitoring for key wastewater sources (such as kitchen, laundry room) rather than only monitoring the main outlet. Node monitoring can use NiuBoL series portable or wall-mounted multi-parameter water quality analyzers.

4.3 Environmental Impact on Treatment Effectiveness

• Difficulty: Low winter temperatures affect biochemical treatment efficiency, and rainwater infiltration dilutes sewage concentration during rainy seasons, leading to reduced activated sludge activity.

• Monitoring response: Add temperature sensors and dissolved oxygen sensors, connect to the control system to achieve dynamic adjustment of aeration rate and reflux ratio. At the same time, set data anomaly alarm thresholds, automatically alert when treatment efficiency falls below set values (e.g., COD removal rate <70%).

4.4 Pipeline Leakage and External Water Infiltration

• Difficulty: Older pipeline networks may have groundwater infiltration or rainwater misconnections, resulting in actual treatment concentrations far below design values, causing inefficient facility operation.

• Monitoring response: Set up conductivity or flow-concentration correlation analysis at the main inlet pipe. Clean water infiltration causes a sharp drop in conductivity, which can be used as a judgment basis.

V. Recommendations for Water Quality Online Monitoring Instrument Selection for Engineering Companies

Based on the above analysis, the following monitoring instrument configuration solutions are recommended for different scenarios of domestic sewage and domestic wastewater:

Selection principles:

• For domestic wastewater pipelines, prioritize low-range, high-precision models.

• For domestic sewage pipelines, instruments must have anti-fouling and automatic cleaning functions.

• All online instruments used for municipal or environmental assessment should have automatic standard sample verification and data logging functions.

VI. Deployment Value of Online Water Quality Monitors in Domestic Drainage Projects

6.1 Compliance Value

Many regions have required key drainage users (such as large residential communities, commercial complexes, hospitals) to install online monitoring equipment and connect data to environmental or housing & construction department platforms. Proactively configuring compliant online monitoring systems avoids later rectification costs.

6.2 Operational Value

For engineering companies undertaking operation and maintenance of sewage treatment facilities, online monitoring data can achieve:

• Remote judgment of treatment facility operation status

• Early warning of excessive discharge risks

• Reduced frequency of manual sampling and testing

• Creation of traceable electronic records

FAQ

Q1: Can domestic wastewater be directly discharged into stormwater pipes?
A: No. Domestic wastewater should be connected to the municipal sewage network and must not be discharged into the stormwater system. In some areas, treated reclaimed water can be used for greening or landscape replenishment, but must meet corresponding water quality standards.

Q2: In combined sewerage projects, how to determine whether ammonia nitrogen needs to be measured?
A: As long as the drainage includes toilet sewage, ammonia nitrogen monitoring is recommended. Ammonia nitrogen is a characteristic pollutant of domestic sewage and a key indicator for environmental inspections.

Q3: Does kitchen wastewater belong to domestic sewage or domestic wastewater?
A: In strict classification, kitchen wastewater belongs to domestic wastewater, but its oil and organic concentration are much higher than hand washing and shower wastewater. In engineering design, it is recommended to pre-treat kitchen wastewater separately before mixing with other wastewater.

Q4: When using domestic wastewater as raw water for a water reuse system, what indicators need to be monitored?
A: At a minimum, COD, turbidity, pH, and conductivity should be monitored. If reused for toilet flushing, residual chlorine also needs to be monitored in the effluent. An online multi-parameter analyzer is recommended.

Q5: How often should online monitoring instruments for domestic sewage treatment facilities be calibrated?
A: COD and ammonia nitrogen online analyzers: standard solution verification recommended every 7-15 days; pH and DO electrodes: monthly calibration recommended. Calibration records should be kept for review.

Q6: Can NiuBoL water quality monitoring instruments connect to third-party SCADA platforms?
A: Yes. NiuBoL instruments standardly support Modbus RTU/TCP protocol, and can also provide 4-20 mA analog output, compatible with mainstream PLC and IoT platforms.

Q7: What indicators need to be monitored at the main sewage outlet of a residential community?
A: Typically, COD, ammonia nitrogen, pH, and flow need to be monitored. Some local authorities require additional total phosphorus and total nitrogen. Specific requirements should follow local environmental regulations.

Q8: How to set alarm thresholds when sewage and wastewater are monitored together?
A: It is recommended to set upper limit alarm values according to domestic sewage standards, and also set lower limit alarm values (e.g., COD persistently below 50 mg/L may indicate clean water infiltration) to troubleshoot pipeline issues.

Conclusion

The difference between domestic sewage and domestic wastewater goes far beyond a name. For system integrators, IoT solution providers, and engineering companies, this distinction directly determines:

• The design and selection of drainage pipeline systems (combined or separate)

• The range and functional configuration of online water quality monitoring instruments

• The selection and scale of sewage treatment processes

• The feasibility and economy of water reuse systems

Against the backdrop of increasingly stringent environmental regulations and rising requirements for water resource utilization, clearly distinguishing the water quality characteristics of sewage and wastewater at the early project design stage, and deploying monitoring solutions accordingly, is a key measure to reduce project risks and improve system reliability.

NiuBoL provides a comprehensive product matrix of online water quality monitoring covering domestic sewage, domestic wastewater, water reuse, and process control scenarios, supporting Modbus standard communication protocols for easy system integration and platform connection. To obtain typical project configuration lists or technical specifications, please contact our engineering support team.

 Water Quality Sensor Data Sheet

NBL-RDO-206 Online Fluorescence Dissolved Oxygen Sensor.pdf

NBL-COD-208 Online COD Water Quality Sensor.pdf

NBL-CL-206 Water Quality Sensor Online Residual Chlorine Sensor.pdf

NBL-DDM-206 Online Water Quality Conductivity Sensor.pdf

NBL-PHG-206A Online pH Water Quality Sensor.pdf

NBL-NHN-206 Ammonia Nitrogen Water Quality Sensor.pdf