Online Analyzers in Wastewater Treatment

Single-Parameter Online Analyzers in Municipal Wastewater Treatment Processes

Introduction

Water is a fundamental resource for our survival. It appears in every aspect of our lives, from serving as a source of food and energy to being used as a solvent, transport medium, cleaning agent and coolant in various industries. However, water not only contains vital minerals and nutrients but can also contain harmful pollutants that lead to physical and biological accumulation. Following municipal or industrial use, water can carry pollution from heavy metal compounds, fertilizers, pesticides, hormones, synthetic products and other substances that pose high risks to public health and the environment, and therefore must be treated before discharge to the environment. Through Municipal Wastewater Treatment and Water Pollution Control Regulations, discharge limits for analytical parameters in wastewater have been restricted to eliminate the aforementioned risks to public health and the environment. These parameter limits, monitored by strict rules worldwide, form the basis of wastewater treatment facility operations and discharge conditions to the environment. Continuous monitoring of analytical parameters is of great importance in preventing problems that could hinder industrial processes. In this context, there is a growing need for online measurement systems that are affordable, easy to use and contain integrated solutions for parameters that must be continuously monitored during the wastewater treatment process. [caption id="attachment_134250" align="aligncenter"] Figure 1. Wastewater Treatment Facility[/caption]

Municipal Wastewater Treatment Processes

In wastewater treatment processes, three fundamental processes can be identified: physical, biological and chemical. Within the framework of these processes, typical treatment facilities use preliminary and primary treatment, secondary treatment and advanced (tertiary) treatment methods in sequence, with the aim of cleaning wastewater to a level that will allow discharge appropriate to regional conditions. While many wastewater treatment facilities use processes based on combinations of primary and secondary treatment methods, in some regions tertiary wastewater treatment methods are also employed to protect ecological life and enable reuse of treated water for various purposes. Preliminary and Primary Treatment Processes Wastewater collected and entering the facility for treatment first undergoes preliminary treatment. This process typically consists of screening/separation and sand removal steps. In the screening/separation step, large-sized coarse objects suspended in water such as bottles, cans, sticks and fabric waste that could damage pumps, narrow pipes and other mechanical equipment in subsequent stages of the process are removed with the aid of screens. Wastewater passing through the screens moves to the next step in sand traps where heavy inorganic solids such as sand and gravel settle to the bottom. High quantities of sand and gravel in the influent to the treatment facility can lead to wear of pumps and mechanical equipment, blockages, and faster filling of tank capacities required for treatment. The preliminary treatment process serves to facilitate the subsequent treatment steps and has low impact on overall wastewater quality. [caption id="attachment_134251" align="aligncenter"] Figure 2. Screening of Coarse Waste[/caption] Wastewater passing through the screening/separation and sand removal steps still contains suspended solids along with dissolved organic and inorganic compounds. Primary wastewater treatment is based on the principle of settling components in wastewater by gravity to remove suspended solids. When wastewater enters the primary settling tank, it slows down and suspended solids gradually settle to the bottom. The solid mass settling to the bottom of the tank is called primary sludge. Various methods and mechanisms are used to subsequently remove the sludge produced as a result of primary treatment from the tanks. Primary treatment can typically remove approximately one-third of BOD and half of suspended solids in municipal wastewater. While the purpose of primary wastewater treatment is to separate easily removable suspended solids and BOD, wastewater components present as settleable solids or absorbed onto settleable solids can also be removed during this process. For this reason, primary treatment also provides some reduction in the concentration of nutrients, pathogenic organisms, trace elements and potentially toxic organic compounds. These removed components remain in the primary sludge.

Secondary Treatment Process

Wastewater exiting primary treatment moves to a process called secondary treatment. In the secondary treatment process, biological treatment techniques are used to remove the bulk of organic compounds and suspended solids. The two most commonly used processes in biological treatment are surface-growing (biofilm) and suspended-growth systems. In surface-growth processes, microbial development occurs on the surface of stone or plastic media. Bacteria, algae and other microorganisms proliferate and form a biomass on the surface of the media. Wastewater passes over the media together with air, and during this process bacteria use the oxygen in the air to consume most of the organic matter in the wastewater as food. Thus, water exiting the media becomes much cleaner. A portion of the biomass stripped from the media is settled in a secondary basin. [caption id="attachment_134252" align="aligncenter"] Figure 3. Aeration Basin[/caption] Suspended-growth processes likewise operate on the principle of biological breakdown of degradable organic compounds and conversion of ammonia nitrogen to nitrate to remove organic nitrogen compounds. Microbial growth occurs in an aerated water mixture into which air is pumped or which contains sufficient mixing to provide adequate oxygen transfer. In the aeration tank, microorganisms are exposed to wastewater in suspension for several hours. This allows bacteria and other microorganisms to break down organic matter in the wastewater. Treated wastewater exiting the aeration tank flows to a secondary settling tank where excess biomass is removed. A portion of this biomass containing millions of active aerobic bacteria can be returned to the aeration tank and reused. The remaining waste biomass and settled solids are processed before disposal or reused as biosolids. [caption id="attachment_134253" align="aligncenter"] Figure 4. Secondary Settler[/caption] Wastewater completing the biological treatment process passes through a gravity filter with a porous structure made of sand or anthracite to remove suspended solids and fine particles still present in it. Particulates are trapped in the pores within the filter media while clear water is transferred to chlorination and dechlorination units to complete secondary treatment. As a result of biological treatment, the wastewater must be disinfected to remove increased bacterial presence and pathogens. The disinfection process prevents the release of bacterial concentrations higher than the established level to the environment. Chlorine is the most commonly used disinfectant type due to its effectiveness at low concentrations and cost. Chlorine can remove more than 99% of harmful bacteria present in wastewater. [caption id="attachment_134254" align="aligncenter"] Figure 5. Water Disinfection with Chlorine[/caption] However, the presence of free chlorine at low concentrations in water discharged after disinfection is quite harmful to the environment. In addition, carcinogenic trihalomethanes and organochlorines that can form as a result of the reaction of chlorine with organic matter in water pose a major threat to aquatic life. For this reason, residual chlorine that may remain in wastewater must be removed before discharge to sensitive water bodies. Dechlorination eliminates free or total combined chlorine residue remaining after chlorination, minimizing the impact of potentially toxic disinfection byproducts. Dechlorination is typically performed by adding sulfur dioxide or sulfite salts. Activated carbon adsorption is also another effective dechlorination method, though more expensive compared to other methods. When chlorine in treated wastewater could be harmful to fish and other aquatic life, alternative options to chlorine disinfection such as ultraviolet light or ozone can also be used.

Tertiary (Advanced) Treatment Process

Tertiary treatment processes in municipal wastewater treatment facilities are applied when higher quality treated water is required in receiving water bodies or for other uses than what is achieved in secondary treatment. Advanced treatment technologies can be applied as extensions of secondary biological treatment to further stabilize oxygen-demanding substances in wastewater or to remove nitrogen and phosphorus. Additionally, tertiary treatment can include physical/chemical separation techniques such as adsorption, flocculation/settling, advanced filtration, ion exchange and membranes for reverse osmosis to remove suspended solids and other pathogenic microorganisms. These processes applied in various combinations enable achieving the desired degree of treatment control in wastewater. With tertiary treatment processes, wastewater that has undergone higher levels of purification and treatment can be reused for municipal, landscape and agricultural irrigation, industrial cooling and processing, and even indirect augmentation of drinking water sources. Analytical Parameters Monitoring and continuous tracking of critical parameters in municipal wastewater treatment facilities is vital for the sustainability of public health and prevention of environmental pollution. In this context, close monitoring is required for compliance of these analytical parameters, which make specific contributions to each stage of the treatment process, with standard conditions established in regulations:

Cyanide and Trace Heavy Metals

When wastewater is discharged from nearby, monitoring parameters such as cyanide may be important to protect treatment operations. Additionally, toxic metals (Hg, Ni, Co, Cu, Cd, Pb, Cr, Zn, Sb) may need to be monitored to determine whether industrial waste is being discharged outside permitted limits. [caption id="attachment_134255" align="aligncenter"] Figure 6. Analysis Points in Municipal Wastewater Treatment Process[/caption]

Phosphorus/Phosphate

Since phosphorus has a highly reactive structure, it readily bonds with oxygen to form phosphates (orthophosphates o-PO4, polyphosphates and organic phosphates). Water utilities are legally obligated to control phosphorus levels in wastewater they discharge due to its eutrophication effects in aquatic environments. European directives have resulted in progressively tightening regulations on phosphorus removal. The 1991 Municipal Wastewater Treatment Directive established a limit of 2 mg/L for larger flows or wastewater discharged to sensitive waters. However, the Water Framework Directive (WFD) adopted in 2000, which focuses on continuous improvement and achievement of "good" status for all water channels, has typically led to the application of limits of 0.5-1.0 mg/L. It is generally thought that limits as low as 0.1 mg/L will be necessary to achieve the WFD's "good" status. For this reason, phosphorus removal will be a major focus for municipal wastewater treatment facilities in the coming years.

Other Parameters

Each wastewater treatment facility has an obligation to monitor various parameters depending on the process stages it has, the limit values of the region to which it discharges, and the desired wastewater quality. Other parameters that can be monitored and tracked in wastewater treatment facilities may include sulfate, sulfur, chlorine, COD, iron and aluminum.

Online Analysis in Wastewater Treatment Processes

Failures in manual sampling or manual analysis processes for critical parameter analysis in wastewater treatment can result in significant production quality and time losses. Considering all elements resulting from potential errors such as operator differences, experience level, sample volume taken, equipment/accessory cleaning, and analysis frequency, the advantages that an online analysis platform capable of enabling automatic sampling, fully automatic analysis, result reporting and alarm transfer at out-of-limit values become clearly evident. Parameter measurements are performed through automatic sampling of the sample and completion of all subsequent analytical processes without requiring any intervention. By automatically transferring the obtained analysis results to PLC/DCS systems and the ease of remote control of the analyzer, rapid intervention in the process is enabled and significant advantages are provided in this context. As Metrohm, within the framework of the experience and knowledge we have accumulated so far on process analysis, and particularly our comprehensive application range that forms the foundation of our global leadership position in the field of titration, we present our 202X Series Single-Parameter Online Analyzer systems suitable for the Industry 4.0 generation for wastewater treatment facilities. The 202X Series Single-Parameter Online Analyzer systems, with advantages such as continuous operation capability, low chemical consumption, reliable 24/7 operation and user-friendly graphical interface, guarantee reliable process monitoring and control, enabling you to save time and costs. 202X Series Single-Parameter Online Analyzer systems are grouped under two main hardware segments: 2026 Online Titrolyzer for measurements based on potentiometric and ISE analysis techniques: [caption id="attachment_134260" align="aligncenter"] Figure 7. 2026 Online Titrolyzer[/caption] 2029 Online Photometer for measurements based on photometric and colorimetric analysis techniques: [caption id="attachment_134270" align="aligncenter"] Figure 8. 2029 Online Photometer[/caption] Both system variants feature striking common characteristics: • Compact footprint providing floor space savings for tight industrial areas, • IP66-compliant secure and robust external housing, • Proven applications across various sectors in a wide range of direct field applications, • Ethernet, Modbus TCP/IP and USB data transmission capability for remote access/control, • System management and trend graphs via 7" full-color touchscreen. Standard Equipment Sets 202X Series Single-Parameter Online Analyzer systems are offered as analyzer equipment sets with various standard system components for analysis and control of parameters present in the wastewater treatment process:

Sampling

In 202X Series Single-Parameter Online Analyzer systems, the sample is brought directly to the reaction vessel via a closed sampling line. Thus, unlike manual sampling, a representative sample drawn from the correct sampling point without contact with the external environment reaches the analyzer. With the 202X system, it is possible to sample from either a single or two different sample flow points.

Reliable Analysis Results

Accurate and reproducible results obtained as a result of measurements performed using 202X Series Single-Parameter Online Analyzer systems demonstrate that the systems can be successfully integrated into every stage of the wastewater treatment facility. The full automation nature of the system brings numerous advantages. In fully automatic online analyses performed compared to manual analyses, errors such as incorrect sampling, failure to identify measurement points, incorrect and non-reproducible results can be prevented. Since all procedures such as sampling, chemical additions, analysis step and recording of results are automatically provided under the 202X system framework, measurement errors, differences between operators and analysis time inconsistencies are eliminated, and due to continuous analyses without manual intervention, labor requirements decrease while operator safety increases. As parameter measurements become more accurate, precise and efficient, disruptions that may occur in the process can be monitored in real time, improvements in quality are achieved and production repetition problems are minimized. 202X Series Single-Parameter Online Analyzer systems transmit all data including ongoing analyses, obtained results, alarms and others to PLC/DCS or other data systems as requested via digital and 4-20 mA analog outputs, Modbus TCP or VNC transmission infrastructures present in the hardware, enabling continuous monitoring of the process and immediate intervention in the event of any disruption. Complete Wastewater Treatment Process Monitoring 202X Series Single-Parameter Online Analyzer systems form single-parameter entry-level systems for different operational steps in the water treatment process. When measurement of multiple parameters together or increase in analysis frequency or measurement points is requested at the treatment facility, higher-level models such as 2035 or 2060 Process Analyzers are offered to achieve comprehensive combinations. With 2035 and 2060 Process Analyzers, in addition to parameters measurable in 202X systems, COD, total/WAD cyanide, total nitrogen and total phosphorus parameters can also be measured. [caption id="attachment_134275" align="aligncenter"] | January - February 2022 Figure 9. 2060 Online Process Analyzer[/caption] Online voltammetric analysis of total arsenic and heavy metals (Hg, Ni, Co, Cu, Cd, Pb, Cr, Zn, Sb) can be performed with the 2045VA Online Process Analyzer.

Conclusion

Metrohm Process Analytics has more than 40 years of experience worldwide in online process analysis. With our installed equipment fleet of over 900 analyzer systems in wastewater treatment facilities in the EMEA region alone, we continue to serve our customers reliably and provide our global experience in the sector. As Metrohm Turkey Process Analytics Team, we can provide comprehensive services ranging from project consulting, engineering and sales stages to analyzer installation, commissioning and training, system maintenance, accessory and spare parts supply, support, service and repair processes. Through our local structure integrated with Metrohm Process Analytics EMEA Regional Center, we are at your side for all your online analysis needs.

References

1) 80005233EN 2026 Titrolyzer/2029 Process Photometer– Powerful and compact single method online analyzers. 2) 8.000.5358EN Metrohm Process Analytics – Online Analyzers for Municipal Wastewater Analysis. 3) EPA, 2004, Primer for Municipal Wastewater Treatment Systems, Washington DC. 4) EPA, 2000, Waste Water Technology Fact Sheet, Washington DC. 5) National Research Council, 1996, Use of Reclaimed Water and Sludge in Food Crop Production, Washington DC: The National Academies Press.  

Şahin Yalçın Sales and Application Engineer Process Analytics / Spectroscopy Metrohm Turkey