Analysis and Characterization of Industrial Wastewater

• 1. Characterization of Industrial Wastewater
• 2. Sampling
• 3. Wastewater Analysis
• 4. Laboratory Tests and Trials                   
• 5. Definition and description of the appropriate process: treatment line
• 6. Sizing of Effluent Treatment Equipment
• 7. Conclusions

1. Characterization of Industrial Wastewater

Wastewater generated by industrial activities must be properly treated in order to comply with current regulations regarding wastewater discharge and environmental protection.

Proper characterization of wastewater is the first step in ensuring the proper design of a wastewater treatment plant. The quality and reliability of preliminary analyses and tests directly determine:

• Selection of the process and technologies.
• Equipment sizing.
• The final performance of the facility.

Insufficient knowledge of the effluent can lead to inefficient designs, operational problems, and difficulties in complying with legal discharge limits.

The configuration and complexity of the treatment train will depend on factors such as:

• The physicochemical and biological composition of the discharges.
• Variability in production processes.
• The requirements imposed at the final point of discharge or reuse.

Each industry has its own unique characteristics stemming from its raw materials, manufacturing processes, auxiliary products, and cleaning operations.

The characterization process typically begins with determining the flow rates of the various streams that make up the total effluent. This is done using direct measurements taken with flow meters, hydraulic balances, and historical water consumption records.

It is also essential to have information provided by the industry itself regarding process water consumption, cleaning water, cooling circuits, internal recirculation systems, production shifts, and possible seasonal variations.

Sampling of the various wastewater streams is then carried out. This work can be performed using automatic or manual systems, always ensuring that the samples obtained are representative of the plant’s actual operating conditions. During this phase, particularly contaminated effluents, separable discharges, and possible options for minimizing or reusing water are identified. In this regard, it should be noted that the most efficient treatment is always the one that first reduces the volume and pollutant load of the generated effluent.

Finally, all supplementary information regarding production incidents, special cleaning operations, intermittent discharges, or the use of specific chemicals is of great importance for correctly defining the characteristics of the effluent and ensuring an appropriate design for the future wastewater treatment plant.

2. Sampling

Sampling is a fundamental step in the characterization of industrial wastewater, as the validity and representativeness of subsequent analytical results depend largely on it. A sample that is improperly collected or stored can lead to erroneous interpretations of the nature of the discharge and, consequently, to inappropriate decisions regarding treatment design.

There are different sampling methodologies depending on the characteristics of the effluent and the objectives being pursued.

Automatic sampling systems are particularly recommended for facilities with high variability in flow rates or contaminants, as they minimize human error and ensure greater statistical reliability of the samples collected. However, in certain circumstances, manual sampling is still performed, especially in preliminary studies or at hard-to-reach discharge points.

Spot or instantaneous sampling involves collecting a sample at a specific point in time and is typically used when the characteristics of the discharge remain relatively constant or when the goal is to detect a specific incident.

However, since many industrial discharges vary significantly throughout the production shift, it is more common to use composite sampling, which combines different samples taken over a specific period of time, usually in proportion to the flow rate.

Flow-proportional sampling provides a much more accurate representation of the actual pollutant load discharged, since it relates the volume of the sample collected to the instantaneous flow rate of the effluent. This system is typically implemented using programmable automatic equipment capable of taking samples at defined time intervals or in response to signals from flow meters, level sensors, or physicochemical parameter sensors.

Sampling is typically supplemented by the installation of dedicated sampling chambers, refrigeration and storage equipment, flow meters, and in-line sensors for parameters such as pH, conductivity, temperature, turbidity, and dissolved oxygen.

Proper selection of the sampling point is essential; areas with sedimentation, excessive turbulence, or incomplete mixing that could affect the representativeness of the sample should be avoided.

3. Wastewater Analysis

Once representative samples of the effluent have been collected, physicochemical and microbiological analyses are conducted to determine the composition of the wastewater. These analyses must be carried out in specialized, accredited laboratories, following standardized procedures and officially recognized methods.

Proper sample preservation is essential to ensure the reliability of analytical results. In general, samples should be kept refrigerated at temperatures close to 4°C and stored in suitable containers that are tightly sealed and protected from light. In certain cases, it may be necessary to add chemical preservatives, provided that they do not alter the parameters being analyzed.

Chain-of-custody control is essential to ensure complete traceability of the sample, from collection through the issuance of analytical results. To this end, the date and time of sampling, the sampling site, storage conditions, and the individuals responsible for each operation must be properly recorded.

The parameters that can be analyzed in industrial wastewater are very diverse and depend on the type of industrial activity being carried out. Among the most common are:

• Suspended solids.
• Oils and fats.
• Chemical oxygen demand (COD).
• Biological oxygen demand (BOD5).
• Dissolved solids,
• Total phosphorus.
• Kjeldahl nitrogen.
• Detergents.
• Heavy metals.
• Color.
• pH.
• Conductivity.
• Temperature.
• In certain industrial sectors, it is also necessary to analyze specific toxic compounds, hydrocarbons, solvents, surfactants, or pathogenic microorganisms.

To perform these analyses, laboratories have specific equipment such as pH meters, conductivity meters, turbidity meters, spectrophotometers, oxygen meters, respirometers, drying ovens, and filtration systems.

In some cases, advanced instrumental techniques, such as chromatography or spectrometry, are used to detect specific contaminants present in low concentrations.

The analytical results obtained serve as the basis for determining the most appropriate treatment strategy and make it possible to establish material balances, estimate pollutant loads, and define expected treatment performance.

4. Laboratory Tests and Trials

In addition to conventional analytical characterization, the design of an industrial wastewater treatment facility requires the conduct of laboratory treatability tests. The purpose of these tests is to reproduce the various treatment processes on a small scale and to evaluate the actual behavior of the effluent when subjected to different treatment technologies.

These tests allow you to:

• Determine the expected performance in the removal of contaminants.
• Optimize reagent dosages.
• Assess the biodegradability of the effluent.
• Select the most appropriate technologies from both a technical and economic standpoint.

Among the most common tests are pH adjustment, coagulation, and flocculation tests, which are used to determine the optimal conditions for separating solids and colloidal matter. Within this group of tests, the “Jar Test” is an essential tool for selecting the most effective reagents and establishing the most appropriate dosages.

In addition, sedimentation and DAF flotation tests are conducted to evaluate the capacity to separate suspended solids and fats, as well as biodegradability tests aimed at determining the feasibility of applying aerobic or anaerobic biological treatments.

In cases where advanced treatment is required, filtration tests using granular media or membranes are also conducted, as well as advanced oxidation and disinfection tests using chemical oxidants or ultraviolet radiation.

Another important aspect is the management of the sludge generated during the wastewater treatment process. For this reason, specific dewatering tests are conducted to properly select the mechanical drying systems (filter press) and estimate the final waste output.

Conducting pilot tests, both in the laboratory and directly at the client's facility, allows us to validate the results obtained and fine-tune the final design of the wastewater treatment plant.

5. Definition and description of the appropriate process: treatment line

Once the characterization and testing phase is complete, the most appropriate treatment process for the effluent under study is determined. This determination is based on the analytical results obtained and on the technical experience gained at similar facilities.

The configuration of the processing line depends on numerous factors, including:

• The nature of the spill.
• The flow rate to be treated.
• Variability in pollution levels.
• Space constraints.
• The quality requirements for the final discharge or reuse of treated water.

In most cases, treatment begins with a pretreatment stage designed to remove coarse solids, sand, grease, and other floating materials that could interfere with subsequent stages.

A homogenization and neutralization system is then typically incorporated to mitigate fluctuations in flow rate and contamination, as well as to adjust the pH to the appropriate levels for subsequent treatment.

Depending on the characteristics of the effluent, it may be necessary to apply physicochemical treatments based on coagulation, flocculation, precipitation, and dissolved air flotation (DAF), which are particularly effective in removing suspended solids, oils, fats, and colloidal matter.

When the effluent has a high biodegradable load, aerobic or anaerobic biological processes are incorporated to reduce the dissolved organic matter. In certain industrial applications, advanced biological reactors may be used, such as MBR systems, nitrification-denitrification processes, MBBR processes, or advanced oxidation technologies.

Finally, when high levels of treated water quality are required, tertiary treatment processes are incorporated, consisting of filtration, membranes, activated carbon, or disinfection using ultraviolet radiation or chemical oxidants.

The resulting treatment process must ensure compliance with established discharge limits, while also meeting appropriate standards for energy efficiency, operational flexibility, and minimization of operating costs.

6. Sizing of Effluent Treatment Equipment

Once the treatment process has been defined, the next step is to design and size the equipment that will be part of the wastewater treatment plant. This sizing is based on measured flow rates, calculated pollutant loads, and the performance results obtained from laboratory and pilot tests.

The hydraulic design accounts for both average operating flow rates and the maximum foreseeable peak flow rates, establishing the necessary retention times for each unit process. At the same time, the process design takes into account the mass loads of contaminants, sludge production, and the requirements for reagents, air, and energy.

In this phase, the volumes and dimensions of the homogenization, neutralization, and reaction tanks are determined, as well as the appropriate sizes for flotation equipment, settling tanks, biological reactors, filters, and sludge dewatering systems.

Pump sets, agitation systems, compressors, blowers, and chemical dosing equipment are also selected, along with all the instrumentation necessary for the automatic control of the facility, including flow meters, pH meters, oxygen meters, redox sensors, and monitoring systems using programmable logic controllers.

The project also includes the development of basic and detailed engineering, construction drawings, hydraulic and electrical schematics, civil engineering drawings, and the programming of automation and control systems.

The entire design must take into account potential seasonal variations in production, the facility’s future flexibility, and the optimization of operating and maintenance costs, while ensuring high levels of reliability and operational safety.

7. Conclusions

The characterization and analysis of industrial wastewater is an essential step in the development of any effluent treatment project. Accurately identifying the characteristics of the effluent, along with conducting treatability studies and pilot tests, makes it possible to develop technical solutions tailored to the specific needs of each industry.

Increasing environmental regulations require facilities that are increasingly efficient and reliable, capable of ensuring compliance with discharge limits while maintaining reasonable operating costs and high levels of sustainability.

In this context, the combination of technical expertise, rigorous analysis, and carefully selected technologies is essential for designing robust, flexible treatment facilities that are equipped to meet current and future demands in industrial wastewater management.

Bibliography and consultations

UNE-EN 12255. Wastewater treatment plants. Technical specifications for the design and operation of wastewater treatment plants.

Ministry for Ecological Transition and the Demographic Challenge. Protocol for the Inspection of Wastewater Discharges. Government of Spain.

Royal Legislative Decree 1/2016, dated December 16, approving the consolidated text of the Law on Integrated Pollution Prevention and Control.

Royal Decree 849/1986, dated April 11, approving the Regulations on the Public Water Domain.

“What are the regulations governing industrial wastewater in Spain?” Technical documentation and industry-specific regulations on industrial discharges and environmental control.

Metcalf & Eddy. Wastewater Engineering: Treatment and Resource Recovery. McGraw-Hill Education.

Tchobanoglous, G.; Burton, F.; Stensel, H. Wastewater Characterization: The Importance of Laboratory Analysis in Wastewater Treatment Plant Design. Technical References on Wastewater Characterization and Treatment Plant Design.

APHA-AWWA-WEF. Standard Methods for the Examination of Water and Wastewater. American Public Health Association.

UNE-EN ISO 5667. Water quality. Sampling. Guidelines for the collection and preservation of wastewater samples.