Water Treatment: The not-so-big step to reclaim
Canada has been endowed with more than 20 per cent of the world’s total freshwater resources — perhaps being one of the reasons we are noted as one of the highest per capita users of water in the world.
However, the water supply is well distributed and not necessarily readily accessible to the 85 per cent of the Canadian population living primarily along the southern border. The easily accessed water supply, while still abundant, is heavily used and can be overly stressed when other users and environmental needs are balanced. And certain geographic areas with arid climates and often under drought conditions can have severe water scarcity in the dry summer months.
There is a growing interest in using reclaimed water within the context of sustainable water management for uses such as irrigation and indirect potable reuse. Nature has been recycling water since the beginning of time, but the hydrologic cycle has a long residency time prior to reuse. The human hydrologic cycle of discharging the treated sewage to surface water bodies or to ground, which gets recycled, can have a much shorter timeline and rely on dilution. Cities located on Canada’s numerous rivers have been extracting water upstream and discharging downstream or to ground, only to affect the next community.
From a practical point of view, if we are required to treat our drinking water, and treat our used water, is there economy in reusing any portion of the water to save on infrastructure costs and maintenance costs?
Think of “Reduce, Reuse and Recycle.” In our own backyard, many golf courses and industrial users are already reusing treated effluent. Is it a big step to go toilet to tap? Despite the advantages of using reclaimed water, pathogens and other constituents in reclaimed water may pose a risk to human health or the environment, if inadequately treated. There are real risks, as well as perceived risks, associated with reuse of water, requiring a high degree of oversight by both the operator and the regulatory authority — often requiring backup options, which can negate the financial benefits. Owing to these risks and the low cost of water in Canada, the pursuit of water reclamation has been slow.
As noted, there is also the negative public perception regarding the application of sewage for urban uses. Stringent water-quality monitoring requirements by regulatory bodies is also a deterrent for smaller developments, as it can be cost-prohibitive.
So where is the right balance for provision of safe, reliable and cost-effective use of reclaimed water? And is it time to push the regulatory envelope to pursue process and monitoring controls to negate the risk perception? Continuous process control and monitoring, in conjunction with the use of reliable equipment, can provide safer reclaimed water. This can also provide a higher level of comfort to the public and regulatory bodies through proof of use. To use reclaimed water, it is vital to have quality, ongoing process-control measures in place to consistently provide good quality effluent.
The biological processes are dependent on physical parameters such as dissolved oxygen (DO), pH and temperature. A small wastewater system can have the operator testing these parameters manually and making decisions for process adjustment. For most part, this produces acceptable results, but does not provide the reliability of automatic monitoring and requires higher operator involvement, and operations costs exceeding the capital costs of equipment over the project life. Larger systems can continuously monitoring the DO in the aeration zone and use a control logic to regulate the blower air proportionately. This results in optimum air at all times, while also saves power. Continuous pH and temperature monitoring can also provide valuable input to operators regarding plant performance and provide triggers for process adjustment. Programmable control logic can be provided to establish control points and alarms. Data logging function also provides valuable information to the operators regarding trends and anomalies.
It can be a regulatory requirement for some wastewater-treatment facilities to have a continuous monitoring system. In addition to the flow, measurement of turbidity provides an indication of an operation’s effectiveness. An online turbidimeter with an alarm for offspecification effluent ensures compliance with the regulatory requirements for reclaimed water. The process can be adjusted to reduce the solids if high turbidity observed (i.e. a coagulant can be added to produce larger flocs, which can be effectively removed in the clarifiers or the outside of the membrane on an MBR system). Trending of the UV intensity, and an alarm on the UV disinfection equipment, can alert operators to provide maintenance on the equipment, such as sleeve cleaning or bulb replacement, to consistently meet the regulatory requirements.
Water-quality monitoring requirements can be onerous, especially for smaller developments, as most urban use category of reclaimed water requires a daily fecal coliform monitoring, in addition to BOD, TSS at a weekly frequency. Fecal coliform samples are usually tested by the membrane filtration or multiple-tube fermentation techniques in the laboratory. In addition to the cost of the test, there is labour cost involved in collecting and delivering the sample to the testing lab. This is especially arduous and cost-prohibitive for remote sites, where charter planes might be required to send the samples to the nearest laboratory.
One option is to set up an on-site laboratory that can conduct the BOD and fecal coliform tests. Another option is the IDEXX Colilert-18 and Quanti-Tray test method for the detection of fecal coliforms in wastewater, which can be conducted on-site but requires some basic laboratory equipment and operator training.
About the author: Mike Seymour has more than 25 years’ experience in water and wastewater treatment for small decentralized systems throughout B.C. He is currently involved with the BC Water and Waste Association. Seymour is also the principal with MSR Solutions Inc. in Victoria. He can be reached at 250.479.5164.