What we consider black water is what is flushed down the drain from the water closet and the kitchen sink.
Let me first break down wastewater and its components. What we see go down the drain can be broken down by its component water quality, and thus opportunity for reuse.
There is rainwater that comes off storm surfaces external to the building that can enter the storm sewers or combined sewers. There is clear water wastes that could be blowdown water from a cooling tower, discharge from a reverse osmosis device or a water softener or even condensate. There is greywater, water that comes from washing your hands, and even the shower/bath or the rinse water from the washing machine. Then there is the rest — black water, the really dirty stuff.
With the codes changing, the opportunities for water conservation and opening up the avenues for reuse, what really gets into the sewers is pure black water. There is less room in the future for dilution, so we have to think of innovative ways of using decades-old sewer infrastructure in this new condition.
What we don’t want
What we don’t need to see is a failed sewer system where the solids fall out of suspension in the collections pipes or where the carbon load is so high that the old wastewater treatment plant can’t cope effectively with the over-strength conditions. In the end, we as taxpayers don’t want to pay for these failures of the system.
Add to this the trend toward intensification, where more of us live in the dense urban environments. I call it condo living, but what it really is, is a change in how we behave in a smaller space, where density offers more opportunities to get innovative.
I will talk about high-rise buildings, intensified landscapes and how it affects our sanitary systems, and what we can do to encourage change to safeguard these systems.
The first thing observed for many condominium communities is the change in lifestyle. The common element is not just the roadway in front of your driveway, but the whole building outside your apartment. This changes how you behave. One of the interesting trends we have seen is the decreasing effectiveness of green-bin programs to get organics recycled. The “yuck factor” of taking your food waste to the garbage room de-incentivizes people to do it. Thus, this stuff goes to garbage or down the kitchen sink. Who cares since it is the common element fees that pay for the jetting of the lines and the general upkeep of the building.
Where once there may have been 10 detached homes and a park, there are now 80 families living in the same space — intensification.
What does this do to the underground infrastructure? Nothing great if not addressed or understood.
As touched on above, people’s very behavior and habits change when things gets squished and compacted. One of the things observed is that their waste habits change. What I call the “yuck factor” increases considerably. The result is that they use their green-bin programs less, they recycle less and either everything goes down one chute or, worse yet, it goes down the drain. In the case of food waste, that is what we see. In these cases, the ability of food waste grinders to divert the organics away from garbage is encouraging. But with that comes the increased fats oils and grease going down the drain from food scraps.
We have been diligent in developing FOG management strategies around food production facilities such as restaurants and groceries, but what’s the effect of those 80 families in a condo putting the three-meals-worth, if not more, of FOG into the sewers?
Condos and intensive living spaces are not required to have a grease interceptor, and yes, I have been known to put my bacon grease down the drain with hot water when I lived in a condo.
That sink is in the kitchen, and if there is a greywater system in place, to boot, then it is only concentrated black water laden with all this fun stuff going down the drain to cause failures.
Add to this the whole flushables issue. Sixty years ago, we simply didn’t flush stinky sanitary wipes, diapers and dental floss down the drain, but we do it now.
My point is simple, add FOG (the glue) plus calcium from the concrete pipes, in a low pH environment with a binder such as dental floss and we have the infamous fatbergs forming. The chemistry is pretty simple.
Are we engineering our own buried infrastructure’s demise?
What we should be looking at as industry and municipal partners is simple. We have done great with traditional FOG programs, managing the threat from the known vectors, but where else can we be taking FOG from to decrease the concentrations in our wastewater? Further, what else can we find to be eliminated as threat vectors in our wastewaters? Flushables don’t come from the commercial restaurant.
I have observed how municipalities are beginning to address this over-strength trend in their wastewater infrastructure. They are smart in upgrading their wastewater treatment plants to capture a lot of this carbon for energy, but what about the lowered flows, the over-strength septage and the chances for fatbergs? What are they doing for the distribution/collection system? These are yet to be addressed and pose a problem not for the wastewater treatment plant, but for the urban flood risk, clogs and failures pose.
If the flows are too low, then the sewage is digesting in the pipes, and that causes smells and, more importantly, the development of H2S and methane. Those are explosive gases we don’t really want in the system. Regardless of movement of sewage to the plant, it will digest, and in an uncontrolled environment, cause a lot of issues later on.
But the hidden danger is the high flow condition risk that we are not exposed to until we have heavy rainfalls or floods. None of this is seen until it fails.
What can we do?
The first thing a municipality should look at is their policies, and see if it is hindering their risk-based models. Then change them.
We could mandate grease interceptors on high-rise residential buildings We could find ways of capturing that organic solid waste at the source to recycle. This may compliment the green-bin program in any jurisdiction by simply capturing what also goes down the drain and add it back to solids organic collection.
In the end, what I am calling for is some research. Organizations such as IAPMO, ASPE and others have done some great research; and companies such as InSinkErator have done excellent jobs of correlating the green-bin effectiveness and food waste grinders in high-rise residential buildings. But we are missing an opportunity here for FOG and possible organic food solids as well if we don’t take good research and turn it into codifiable regulations.
Getting this stuff out of the black-water system from all major vectors allows our original wastewater plants to do their jobs, it safeguards the buried infrastructure, and it eventually safeguards the changing objectives we have as we design buildings on top of old infrastructure.
Note: The views expressed here are strictly those of the author and do not necessarily represent pme or BNP Media.