More and more, our engineering practice is being asked to help clients incorporate green products and strategies into our plans and projects. The clients expect that certain innovative technologies or approaches will make the world a better place. Here, we will look at a couple of these alternatives using some examples from building/structures and water/wastewater treatment.
Remember that the mantra of the day is “reduce, reuse, recycle.” To begin, we ought to recall the goals of this program in the first place. Depending on who you ask, it could include either or both of the following ideas:
All in all, metropolitan areas have done the best job in reforming the American psyche with regard to self-sorting consumer waste. These urban areas are strapped for space at landfills and are not inclined to pass the increased tipping fee cost directly to residents. In response, they have instituted far reaching efforts to get the waste sorted before it reaches the curb. The good news is that it appears that the direct per capita landfill tipping volume is holding steady or is down slightly over the past decades — despite a growing population. The not-so-good news is that there is a new source of waste products which has emerged just as the sorting efforts have succeeded. That new source? The recycling collection centers themselves!
It seems that the education efforts have outstripped the technology and industrial processes that make the reuse and recycle of sorted items cost effective. You can liken this to the industrial production of diamonds or the manufacture of gold from another metal. The energy, time, and effort are more expensive than the cost of mining diamonds or gold naturally. There is no market incentive, then, for manufacturers to use “old” containers. Many recycling processing centers find themselves awash with carefully sorted, processed post-consumer “raw” material that gets sent to the landfill anyway for a lack of space.
Have you noticed the little note on recycled plastic and paper things that says, “Made with X percent post consumer content”? You may wonder, “If this is recycled, why isn’t it 100 percent postconsumer content?” It turns out that each time either plastic resin or paper pulp is worked, the tiny stringy fibers that give strength to the product shorten. In turn, this makes the final product weaker. Even in recycled products, some previously unused base product is included in the mix. For some applications, any “used” material contributes a level of unpredictability which consumers will not accept. This is why paper grocery sacks are often made of virgin pulp — newly cut trees, not last year’s phone book — and why used plastic grocery sacks aren’t incorporated into structural plastic lumber. In both of these green products, new base materials are used to produce a consistent quality product for their intended markets.
So while using “plastic lumber” means that although trees weren’t cut down specifically to make the new decking, there were no old grocery sacks kept out of the landfill either. The base material is a hydrocarbon polymer produced from crude oil with all of the environmental and energy issues associated with petrochemical plants producing gasoline or home heating oil.
Reusing some of the product material will lengthen the time before it ends in the landfill and reduce the amount of new material which has to be manufactured. This is precisely why we recommend that existing structures made from pressure treated (CCA) lumber be dismantled and reused rather than demolished and dumped. Taking out nails, sorting, stacking, and reusing lumber is not easy. It is labor intensive and time consuming and will likely cost more than buying new materials — if you can find them. Since nothing lasts forever, however, all of these will end up as waste in some form or another. We have only delayed its arrival there.
What about glass? The advertisements tell us, “It’s perfectly clear: Glass Recycles.” Demand for color-sorted crushed glass (called “cullet”) is often far, far outpaced by supply. Since carefully sorted and uncontaminated postconsumer glass containers can be melted and remade at considerably lower temperatures than processing glass from raw materials, this is one area where the effort at the curb pays off for the environment. It’s important to be aware that single color cullet (clear, green, or amber) is much more valuable than mixed cullet — with the most valuable being that which is free from dirt, stones, and other contaminants which will appear as defects in the final recycled product. In short, given glass’s resistance to decomposition, this is certainly one material which we should work hard to keep in circulation — and out of the landfills.
Take note of the distinction above about the material being color sorted. Does your collection and sorting scheme include the sorting of colors of glass? Once intermixed color glass containers are broken together, sorting becomes a cost prohibitive, needle-in-the-haystack exercise. This mixed glass cullet is normally ground down, and its value drops to nearly zero. After all the time, labor, and energy spent to collect and process, it actually has negative value.
One innovative use of mixed glass cullet is for filter media in water filtration plants — swimming pools are included here — and wastewater treatment plants. Historically, natural sand has been used to provide a surface on which microbes live and reduce nutrients in the wastewater to elemental components, detoxifying it for release back into the environment. The problem is that most quarries have difficulty producing sand which meets the pretty stringent requirements for sand media in terms of the particle size distribution and detritus content. Municipal glass crushing facilities, however, generally seem to be producing a material acceptable for installation with a minimum of additional processing. And as mentioned previously, the mixed color cullet has almost no value to container manufacturers, so most facilities end up dumping this crushed material in a landfill at relatively high cost. In short, they’re likely to sell it really cheap! If your facility has a surface sand filter as part of its wastewater treatment scheme, this may be an option. Check with your regulating agency which issues and maintains the discharge permit to see if they have provisions for this media, and perhaps even certified stockpiles or producers.
What about wastewater treatment itself? There has been considerable interest in technologies that are “more natural” than the “traditional” alternatives — septic trenches, sand mound systems, and stream discharge plants, to name a few. As addressed in earlier articles, the decomposition of digestive waste is as natural a process as there is. Under the best circumstances, nature can be left to take its normal course and after a time, the waste is reduced into elemental components and is without biological pathogens. Were this not so, the forest would be filled with . . . well . . . stuff. But when the occupying population exceeds the available land space and time for reduction, the pathogens often cause fatal disease outbreaks or even epidemics. The population is reduced automatically to levels which can be sustained by the land. Camps and conference centers are by their nature, community experiences — concentrating people (and their wastes) to relatively small areas. Allowed to run its course in this case, the natural waste reduction process would present a catastrophic public health crisis.
Modern wastewater treatment relies on the same natural biological mechanisms, but adds components — at least air, in most processes — which may be consumed completely before the nutrients are completely converted. By centrally collecting the waste, containing the treatment to a specific area, adding nutrients at specific times in the process, and monitoring the resulting products, the detoxifying processes are confined, accelerated, and pushed toward completion more safely and consistently. None of this implies that this is a simple process. Quite the contrary is true. The more concentrated the treatment plant and process becomes — that is, the number of gallons being treated per square foot of treatment plant — the more skill is required to manipulate the process times and ingredients to get the desired level of treatment. All in all, though, the modern treatment plant digestion process is as natural as it gets and, when properly operated, delivers predictable, permit-compliant discharge.
What about other natural processes for wastewater treatment? In the past several years, we have been asked to consider several of these natural systems. These have included engineered wetlands and similar setups inside greenhouses. Although research on these methods continues, the Environmental Protection Agency and state regulators have not included these arrangements in rules that govern wastewater treatment for a number of reasons. First, the majority of the engineered wetlands being studied are not being used as primary treatment, but as a final stage before the water is released to a stream or other water body (known as “polishing”). That is, there is normally a traditional wastewater treatment plant upstream of the wetlands. Second, when compared gallon for gallon of treatment capacity, wetland systems are substantially larger than their conventional counterparts, which are often measured in “square feet” as opposed to acres for wetlands. Next, the highly sensitive nature of wastewater reduction by plant roots in the wetlands is difficult to predict and quantify when the flow rates, constituency, and weather conditions all play a most critical role in the conversion of nutrients in waste water. Regulators, tasked with preventing degradation of their region’s waters, are reluctant to permit such an unpredictable process. Along that same line of reasoning, engineered wetlands are typically permitted to be designed with a polypropylene or polyethylene liner underneath. This prevents the unmonitored wastewater from being leaked into — and perhaps contaminating — the ground water table beneath. Lastly, the lack of documented, full-scale operational, industry-based experience with these sorts of systems makes them appear to be a liability from a permitting and regulatory standpoint (EPA 625/1-81-013; EPA 8