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Right equipment helps WWTPs cope with unknowns of septage receiving

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By Christa Renouard

Septage systems that are appropriately designed and maintained provide an excellent form of localized wastewater treatment. If a system gets overloaded or is not on a regular schedule of service, then issues with contamination of surface or groundwater begin to emerge.

A critical component of the proper maintenance of a functioning septic system is to regularly clean and extract settled solids from the tank. However, disposal options for collected septic waste are narrowing to facilities that can handle and pretreat the wastes. Strict regulations and guidelines restrict landfill or land application without the material first undergoing some form of pretreatment.

Wastewater treatment plants provide a viable option to accept and process the collected septage. However, the sheer concentration of the transported sludge can potentially cause plant upsets in smaller facilities. Early strategies where septage was simply dumped in at the headworks, often overwhelmed the screen and caused problems downstream. The end result was many small plants choosing not to accept septage waste.

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By creating a receiving area for hauler trucks to offload septage waste, it becomes practical to employ forms of pretreatment, monitoring and storage. This then allows the plant operations staff to control and meter extra loading to the plant. Systems like this can be automated, reducing the need for excessive operator attention. An accurate billing system can be employed through a keypad/card kiosk that combines the measured flow and monitored water quality parameters in the billing.

The advantage of this approach is that it opens up an opportunity to generate revenue, which offsets the investment and contributes to reducing overall operating expenses.

What was once a problem

Similar to the evolution of handling septic wastes with the creation of septage receiving stations, this same receiving station technique can be modified to accept energy-rich waste grease from restaurants and processers. With early adoption of processes like co-generation, organics such as fats, oils and grease, were sought out to add to the digesters used in generating energy to offset operational costs.

This new approach instituted programs of point source collection techniques for early capture of the grease in localized traps. This also greatly aided in minimizing maintenance issues with grease clogging a municipality’s collection lines and lift stations as the wastes are transported to the wastewater treatment facility.

However, much like the early attempts with the acceptance of septage, grease has its own factors that affect the ease and practicality of accepting these wastes at the facility. One wastewater treatment plant experienced initial difficulty with the handling and processing of received brown grease waste. The grease collection process was susceptible to people treating the collection bins as trash disposal.

The initial design of the receiving station utilized a bucket strainer, which required frequent manual cleaning that diverted operations personnel from essential plant duties. This manpower issue was easily resolved by incorporating a self-cleaning inline sludge screen. This configuration provided a robust technology that fits well into the automated system.

Not without challenges

As a greater diversity of hauled wastes are being accepted into septage receiving stations, so too are the occurrences of unplanned material entering the system. The industry has been served well by standardized septage receiving stations. Many of these systems were designed to accommodate domestic septic tank waste from households, apartment complexes, resorts, etc.

Chemical toilets, or Porta-Potties, present a new challenge. Whereas the nature of a conventional septic system’s waste characteristics minimizes exotic debris in hauled waste, Porta-Potties are a potential wild card. This type of portable chemical toilet provides a sanitary solution for almost any outdoor event. However, this also provides a portal for disposal of just about anything imaginable.

One wastewater treatment plant discovered firsthand what could be encountered with the introduction of waste from portable units. The first system was designed for traditional septage as well as grit. After a series of large public events, there was a sizable influx of wastes brought in from the portable toilets. The receiving machines at the septage receiving station were quickly overwhelmed and disabled.

In troubleshooting, what had come in from several portable units around the area was examined. Everything was found in the septage, from knives, ammunition and power tools to clothing, syringes and electronic devices.

With a clear understanding of the nature of debris being encountered at the facility, it was then possible to provide an addition at the station that could handle that type of waste without causing problems with the machinery. The solution was a centre feed drum type of machine that could handle the severe and unusual material brought in with the portable toilet wastes.

What’s next?

As landfill space becomes scarce, the discarding of wastes becomes increasingly problematic. As costs increase and available space decreases, incentives are emerging to process the so-called “waste” and begin recycling the useable material. One such solution is found with the development of a receiving station that can accept vacuum truck wastes. It is typically made up of a variety of organic and inorganic material, as well as coarse and fine grit, and gravel. This material commonly comes from activities like street sweeping or construction sites.

By combining a series of known technologies, it is possible to accept the wastes into a centralized complete grit treatment facility. This type of system handles, washes and classifies the raw material. As a result, the classified inorganic material (sand and gravel) can be recycled for clean fill or roadbed material. The organics can be retrieved for co-digestion purposes. The net result is captured resources, and the remaining material for landfills is substantially reduced.

With a proper understanding of the materials and wastes to be handled, many possibilities open up. As we shift more from waste to resource recovery, we will creatively provide solutions for the continued emergence of a circular economy.

Christa Renouard is with Huber Technology Inc. This article appears in ES&E Magazine’s February 2020 issue below.

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