The Water Audit: a Tool to Manage Operational Costs and Performance

The goal should be to improve system performance when you identify alternatives such as saving water, for example, so that you maximize production efficiency, ensure the highest product quality and increase operational control.

The audit team must be free to challenge standards and guidelines, and must be encouraged to think outside the box of conventional wisdom. Observations and checklists can be valuable, especially when they represent a new set of eyes, but a high-impact audit will require much more detail and data.

Audits are designed to address specific issues or to measure operating parameters. Typical operational audits address these common issues related to plant operation:

• Quality control/assurance and trademark protection
• Regulatory compliance
• Water conservation
• Selection of water and wastewater treatment technologies
• Wastewater characterization and biodegradability
• Reduction of plant effluent surcharges
• Cost reduction/Cost avoidance
• Higher Efficiency
• Plant Safety
• Sanitation

Case Study Examples

The following three case studies discuss audits related to water treatment, wastewater treatment, water reclamation and plant operations.

Case Study 1

A large multi-beverage plant in Europe with seven production lines was using coagulation and reverse osmosis (RO) membrane technology for product water, cation exchangers for softening water used in heat exchange equipment and for rinsing operations, and aerobic wastewater treatment technology with natural tertiary polishing.

The plant had three issues that needed to be addressed by an audit. First, it had performance difficulties with wastewater treatment: Biochemical oxygen demand (BOD) removal was not at the normal high level prior to the tertiary stage. Second, regulatory compliance at the site required a maximum discharge BOD5 of 20 mg/L plus wastewater to meet many drinking water parameters. The chloride level in the discharge from the plant was borderline high and increasing. Third, the water treatment plant contained four carbon purifiers, one of which was experiencing periodic chlorine carry-through. Even when the plant changed the carbon bed, the chlorine would find its way through shortly after the recharge.

Audit Results

Tests confirmed that a new grade of “line lubricant” the plant was using was interfering with wastewater biodegradability. The plant had purchased a line lubricant that contained an inhibitor to reduce microbial growth, which it did quite well. However, when it washed over into the wastewater plant, it also slowed down the microbes there, which affected BOD and COD reductions. After the audit, the plant switched to a different product.

BOD5 reduction was returned to performance level at 99 percent. However, reducing the chloride level required two alternative approaches: RO water was used where it was not needed. This increased both the volume of water to the wastewater treatment plant and the chloride level of the wastewater. Correcting this, in addition to alternating between softened water and using complexed phosphates for some rinse water applications, resulted in compliance.

In the future, the plant would use RO water only where needed and strictly control water management to minimize chloride levels in the plant effluent.

Chlorine carry-through was traced to an error in carbon purifier design, where insufficient freeboard was allowed for proper backwashing of the carbon. This caused channeling of the carbon bed. The solution was to remove some carbon, creating the proper freeboard, and also to run the unit at a proper design flow of 1.0 gpm/ft3. The backwash rate was increased to 2 gpm/ft2.

Case Study 2

A large food plant in the United States with four production lines was using RO technology and support systems for production water, as well as water softening for water used in heat exchange equipment. The plant was not using wastewater treatment equipment, and had a BOD5 to drain at 2,000 mg/l+.

The plant had three issues that needed to be addressed by an audit. There were substantial sewer surcharges and compliance issues that resulted in the need for a complete wastewater treatment facility. It also had space and zoning limitations, and was considering a new site. The plant was targeted as a significant “user.”