top of page


by JOHN MARTELL, Associate AIA LEED AP, Senior Laboratory Planner, Ci Design, Inc.

Facilities that use a significant amount of chemicals, including commercial and academic research laboratories, manufacturing facilities, and food processing plants, require special planning for lab waste pH neutralization systems. These systems treat wastewater by adjusting the pH to a neutral range, typically between 6 and 9, before discharging the water to the public sewer. 

There are two main methods by which this pH neutralization occurs: active and passive. Read on to learn more about each process and the design requirements for incorporating these systems into a facility.

[For more Science & Technology articles, visit our blog.]



Lab waste pH neutralization systems should be incorporated into the overall design of a facility and coordinated with plumbing, engineering, and local code compliance requirements. These standalone systems are often located in a mechanical space or plumbing room in the lower levels or basement of a facility. Most importantly, they must be placed above city waste systems to allow the waste—once treated, neutralized, and tested multiple times—to flow into the city sewer system.

All materials used in these systems, including the holding tanks and pipes, must be chemical-resistant.



A passive system consists of calcium carbonate (CaCO3) in the form of limestone chips in a single tank. This is a flow-through arrangement which increases the pH level of acidic waste streams. While pH neutralization systems range in size from 1GPM up to 1,000GPM, the tank of the limestone chip systems should be sized based on the number of lab sinks that feed into it.

Limestone chip tanks have a wastewater inlet pipe from the building’s laboratory waste system which releases the effluent at the bottom of the tank. The effluent percolates up to the surface through the limestone chips and is drained off through outlet piping near the surface. The pH level of the effluent is monitored upon leaving the tank as it proceeds to the building’s sewer system.

This passive system is limited to facilities that have relatively low pH waste streams or non-concentrated waste dumps. An advantage of limestone chip systems is that they are relatively inexpensive and do not need to be a centralized system; multiple systems can be installed to handle several gravity-fed waste streams in a facility. However, it is important to note that the limestone chips will break down over time and eventually reduce the system’s effectiveness. In order to replace the limestone chips, the system must be shut down, which could also require the facility to pause some of its operations.



There are two types of active pH neutralization systems: Batch and Continuous Flow. Both system types automatically add acid and/or caustics to neutralize the effluent passing through them.

Active pH neutralization systems capacities range in size from 1GPM up to 1,000 GPM. The treatment tanks are constructed of HDPE (high-density polyethylene), regular polypropylene, stainless steel or fiberglass. The size of the tanks can run from about 500 gallons with some larger HDPE tanks reaching 2,500 gallons in size.

Both types of active systems have many of the same components, including:

  • Treatment tank with a mechanical agitator/mixer

  • In-tank pH sensor

  • In-tank level control

  • Metering pumps for the injection of acid and caustic injection

  • Automatic drain valve

  • Control panel


In a Batch system, the treatment tank fills with effluent over time. When the effluent in the tank reaches a certain level, the batch cycle begins. The agitator activates and the acids or caustics are added until the pH in the effluent is measured and is within a pre-determined range.

When the desired pH level is achieved, the treated effluent is discharged from the tank. Once emptied, the tank is ready for the next cycle and can begin to refill with the effluent of the next batch.

A batch treatment process usually requires between 15 and 60 minutes to complete. An additional, smaller collection tank may be required to store the incoming waste being generated while the treatment tank is in its treatment cycle. This collection tank would require its own valves and pumps that are coordinated with the batch tank to transfer its effluent on demand.


The other active system, called the Continuous Flow system, uses the same mixer, pH sensor, and metering pumps as a batch process, but does not require the automated discharge valve/ pump or the level control to run the system.

This multi-stage system requires multiple tanks with separate sets of metering pumps and automatically treats the effluent as it flows through each tank. The treated pH neutralized wastewater is passed under gravity flow conditions to the final pH monitoring devices before continuing through the pipeline to the sewer system.

When selecting between active pH neutralization systems, it is important to consider that equipment failures in a Continuous Flow system, especially in the metering pumps or the monitoring probes, will not prevent an out of spec discharge. In a Batch system, however, the effluent will not be discharged until the proper pH levels are achieved.



For commercial and academic research laboratories, manufacturing facilities, food processing plants, and other facilities that use a significant amount of chemicals, it is important to incorporate one of these pH neutralization systems into the program. Active and passive pH neutralization systems allow chemical wastewater to be treated properly to a neutral range, according to environmental legislative and quality standards, which ensures that is safe to be released into the public sewer system.

Interested in learning more? Ci Design’s architects, designers, planners, and project managers have unparalleled expertise designing laboratories and other science and technology facilities. Contact our team to learn how we can help.


bottom of page