Economically Self-Sustaining Bioremediation for Lakes

This is going to be long (quasi-Vernonish), but bear with me. If you have any interests in the following, please keep reading:
- ecology
- recreational water use
- politics of locally sustainable economies
- civic projects

In the recent decade, it has become very popular around these parts (Central Plains region of the US) to attempt remediation of ecologically damaged lakes and streams. The causes of this damage are rarely discussed, but probably the largest factor is modern agricultural practices. The effects include diminished water clarity and quality, reduced diversity of plants and animals, increased population of undesirable species (carp, weeds, mosses), with concomitant decreases in recreational use and property values, and further consequences on local economies due to diminished recreation-driven income.

These remediation efforts largely consist of dredging to remove years of accumulated detritus (agricultural run-off) followed by intensive fish and plant stocking. The aim is to increase depth, improve clarity, and begin natural processes to restore chemical and nutrient levels to near normal conditions.

Remediation of this sort gets very expensive. For a small lake (under 500 acres) costs will run around 3 to 4 million dollars (US). This money usually comes from local fundraising (lake homeowners associations), some civic coffers (justified by anticipation of increased tax revenue with higher property values and return of recreation spending), and matching funds from state and/or federal programs.

So what's wrong with this?

(a). The money is a "sunk cost" - nothing is actually purchased, it pays for services rather than goods, and it is spent on the hope of future returns which may never come.

(b). It is a one-shot effort. There is no long-term management plan. The causes of degradation are never addressed. So it is likely that in 5, 10, or 15 years the water will return to its degraded condition.

So here's my proposal:

1. Use some money - say $50 - $100,000, for hydrological and ecological studies so a complete picture of the specific lake in question can be formed.

2. Select a site on the edge of the lake for locating the filtering facility. About 90 acres should do.

3. Buy a couple of suitable, large pump systems (quantity depending upon need).

4. From the hydrological survey, determine ideal locations in the lake for permanent installation of pump intake sites. These should be chosen so that the flow of water from the filtering plant back through the lake will create natural bottom-scouring currents as the water flows back to the intake sites.

5. At the filtration plant, the pump effluent (lake bottom sludge and water) will flow over a slanted slab of concrete on which moss is cultured over a sand substrate. The moss and sand will filter the water as it flows through. Filtered water flows off the slab back to the lake. Depending upon the size of the project, several different filter slabs will be made. A minimum of 2 is required: 1 for active filtering, while the other one is growing the moss culture.

6. The moss/sand culture will absorb not only the silt, but also some of the free nutrient in the lake water (ag runoff creates overnutrification of the water).

7. When the moss/sand has reached the limit of its service life, the eflluent is directed to the next filter slab (which has a freshly cultured moss/sand bed). After a couple of days for open-air drying, the moss/sand/silt/nutrient mix is scraped off the slab. The slab is then prepped for a new culture.

8. The moss/sand/silt/nutrient mix is exactly what potting soil is. So the filtering plant will also have equipment for taking this wonderfully rich soil and packing it in 10 or 25 lb bags. It can also be sold in bulk. This is the source of revenue for the plant's continued operations.

That's it in a nutshell. Here's a summary of advantages of this method over the one-shot expensive approach:

- economically self-sustaining
- on-going, long term management for continuous improvement, rather than one-shot approach
- injection of money into the local economy through employment and service fees


And for you anal types, here's an order-of-magnitude picture of the figures involved:

- Cost of traditional reclamation: $3-4 million USD for 500-acre lake

Ecological and hydrological assay: $100,000
Concrete slabs: $20,000
Pumps: $250,000 (2@125,00 ea.)
Piping, valves, etc: $250,000
Bagging machine: $200,000
Misc. equipment (bobcat, etc.): $300,000
Facility (a building): $100,000

That's about 1.25 million startup costs. Which would leave 1.75 mil for operations until profitable:
Monthly expenses:
Payroll: $6,000
Utilities: $4,000
Maintenance: $5,000
Miscellaneous (chemical testing, etc): $3,000

So that 3 million would cover all startup costs, plus 8 years of operating expenses.

Oh, one last thing: Potting soil is about $0.30 /lb. wholesale ("cheap as dirt") [granted, prices will vary greatly in different areas]. Operating expenses would be covered by selling only 600 lbs per day.