Wastewater Treatment Technologies

The Detroit Water and Sewerage Department (DWSD) employs the activated sludge method of wastewater treatment.  This is a biological process that uses air and a floc composed of bacteria and protozoa.  The end products are cleaner (but not drinkable) water, sludge and gasses (that aren’t captured).

Anaerobic digesters are a more common technology used in such facilities.  Anaerobic digestion occurs naturally.  “Anaerobic digestion is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.”  Along with water and other things, it produces methane, which is captured and used to generate electricity.  

In Orange County CA, a system which cost less than $500 million recycles wastewater to drinking water in three-steps: microfiltration, reverse osmosis and ultraviolet light with hydrogen peroxide. It’s expensive to operate, but not as much as desalinating seawater.

Singapore has adopted a similar wastewater treatment procedure for application after conventional methods.  Its NEWater technology produces extremely pure water that is sold for special industrial uses or mixed with reservoir water and treated in the customary manner for drinking.

Fines and Fees Alone Won't Improve Water Quality

Are some local governments more interested in the revenue from fines and fees for environmental transgressions than achieving the underlying environmental goals?

Consider, for example, the fees charged to businesses for maintaining impervious surfaces like roofs and parking lots from which stormwater or snowmelt rushes to city sewers, burdening wastewater treatment plants.  Why aren’t those businesses motivated to install rain gardens and porous paving?

Or consider the apparent preference in many cities to fine construction contractors for silt running off bare ground or piles of excavated dirt into storm sewers during rainstorms, clogging the sewers and complicating wastewater treatment processes. 

From Macomb County Public Works website: "This is a portion of the 200 tons of sediment and debris that was removed from the Sharkey Drain..."

If contractors were compelled to install silt fencing between the exposed soil and city drains, then, region wide, thousands of tons of silt would be kept out of the sewers.  The willingness of contractors to pay the fines rather than remedy the problem indicates to me that the fines are too low.

UPDATE: SILT FENCE BEST PRACTICES

In many municipalities, mayors, city managers and council people give loud and frequent lip service to environmental concerns and pass a multitude of resolutions and ordinances, but in the municipal departments where the rubber hits the road, those concerns and resolutions and ordinances often get short shrift.

Too frequently, those who do the legislating seem to think that’s the end of the problem, that their intent will be self-executing.  Either that or the city poobahs are throwing around terms like “environment” and “green” and “water quality” merely as cheap public relations gimmicks.

To meet and overcome these challenges, constant public vigilance and action are necessary.

Of Trees, Stormwater and Boondoggles

The Detroit Water & Sewerage Department (DWSD) spent years in collaboration with the Southeast Michigan Council of Governments (SEMCOG) getting ready to plant trees in Detroit neighborhoods and parks as part of a larger plan to control combined sewer overflow.  Scores of meetings were conducted and thousands of personnel-hours expended. DWSD contracted with Greening of Detroit, a non-profit organization, to do the actual planting.  

In a typical year like fiscal 2012-2013, approximately 1500 trees were planted over several weeks in the fall and another 1500 over several more weeks the following spring.  

All three organizations knew or should have known that, at the rate of 3000 or so trees per year, they wouldn’t even be replacing the trees in the watershed that are lost every year through blight, wind, rot, insect infestation, lightning and old age.  

Thus, combined sewer overflow (the justification for the project) is not reduced by a single drop.  I would love to see what the actual total cost of this boondoggle is.

The inclination of DWSD, SEMCOG and Greening to plant trees sparsely along residential streets and in city parks suggests to me that those organizations are more interested in the decorative value of planting trees, much like the city’s discontinued neighborhood beautification program, only now it’s being paid for by DWSD’s ratepayers, as well as taxpayers generally.

Compare the work done privately by John Hantz of Hantz Woodlands.  He, too, spent several years jumping through hoops to get his tree planting project approved by the city. He assembled some vacant city lots, rounded up 1200 volunteers and on one Saturday last month, planted 15,000 trees.

Impressed?  Then look at this.   A private-public partnership in New York City had anticipated planting 100,000 trees per year with a goal of one million trees planted by 2017.  But they’re almost at 900,000 now, so they’ve reset the completion date to 2015.  Granted, Detroit is no New York City, but consider how NYC did it.  They organized with the help of one auto company (Toyota), several foundations and a very active celebrity.  Detroit has all of that and more.  It’s just a matter of how it’s put together and by whom.

We deserve a bigger bang for our buck.

DWSD and Polluted Storm Runoff

Using Green Infrastructure to Reduce Combined Sewer Overflow

One of the principal functions of the Detroit Water & Sewerage Department (DWSD) under its NPDES permit is to control combined sewer overflow (CSO) following rainstorms.

Combined sewers carry both human waste and storm runoff.  Heavy rains cause flow in these sewers to overwhelm wastewater treatment plants.  The polluted effluent then contaminates lakes and streams, threatening public health and damaging the environment.

In some large metropolitan areas, huge underground reservoirs or tunnels have been built to hold polluted storm runoff until the treatment plant catches up.

Several years ago, such a reservoir was contemplated for Detroit, but the city couldn’t afford it.  The plan was scaled back, but not enough to be within the city’s ability to pay for it.

State regulators worked with local officials to develop plans for a number of smaller, surface containment facilities.  They would hold the initial, more contaminated runoff (so-called “first flush”) until the treatment plant could provide both stages of treatment, disinfection and solids (sludge) removal.

Under this last plan, the remaining storm surge (after the first flush) would be disinfected and released to public waters without removing most of the solids.  Nutrients in the solids generate algae growth which in turn depletes oxygen downstream.

In addition, the plan to control overflow called for the application of enhanced natural processes to absorb or at least slow down storm runoff.  These processes are commonly known as “green infrastructure.”

State officials included short, vague references to green infrastructure in DWSD’s proposed NPDES permit renewal.  Green infrastructure was intended to reduce CSO by 10 to 15 percent.  (In my opinion, green infrastructure has the potential for much greater CSO reduction than that.)

The Southeast Michigan Council of Governments (SEMCOG) was enlisted to assist in fleshing out more precise detail concerning green infrastructure.  The effort got off to a slow start, but environmental organizations, notably the Sierra Club, helped to keep the project on track.

Today, as the result of city-wide publicity and neighborhood organizing, some of this green methodology is being implemented.  Trees are being planted, downspouts disconnected from sewers and rain gardens established in backyards and on roofs.  Soon, we can expect to see roadside swales created and pervious concrete used for roads and parking lots.  

Some suburban communities have been reluctant to adopt measures like these, but public interest in clean waterways and stable water services rates will drive improved storm runoff control.