Oh, crap, wastewater again

I recently we communicating with somebody about wastewater treatment as it might apply to a rural Project in Nicaragua and thought I would post some notes here. Anyone who has real world experience in Nic might want to add in their comments. First Nicaraguan cities tend to have sewer systems connected to a local treatment plant, so if you are in an area that is covered by sewer you will be expected to hook up. From what I have seen in Esteli, it looks like they have ponds to give secondary treatment (removal of most of the solids) and them dump the almost clear but very polluted effluent into the river where it mixes with rainwater and is diluted on its way downstream.

If not, you will probably put in a septic system which is tried and true old technology. Details may vary, but typically it is something like the following. Your wastewater goes into an underground tank with 2 compartments. The solids in the wastewater tend to fall and settle in the bottom of the first tank where they will decay through natural anaerobic processes. This is a stinky thing, but because it is below ground and below water, you will not smell anything. The process costs nothing, uses no electricity, etc. Next the water will rise up to a height where it will flow over a baffle (wall) into the second compartment. The same process continues here, but with fewer solids as most of these were captured in the first tank. The ever-clearer water then rises until it flows out the discharge pipe to the leach line, which is a pipe perforated with holes so that the water can be distributed in the trench which was backfilled with crushed rock and then covered with soil. This water is also quite stinky and bacteria laden, but again it doesn`t matter because it is below ground. A properly designed and sized septic system properly installed on the correct type of soil will give problem free service for decades. Having the solids pumped out every 4 to 5 years is somewhat of an option—my experience is that a system not abused by toxic chemicals may go decades without a pump. 2 tips to keeping the system healthy are to not put cooking oil down the sink and run your washing machine effluent somewhere else to keep sand and dirt from building up in your tank.

By the way, that reminds me: modern wastewater is not what you think it is. It is less than 1% solids, and of the solids only a small portion is human waste, as in crap. The rest is food particle, soap, dirt, toilet paper, and ``plastic goods`` etc. Isn`t ``plastic goods`` a cute name for tampon applicators and other junk that gets thrown in toilets? And human waste is by far not the worst thing in a system—grease, such as from hi-volume restaurants, is the worst thing. It coats the tanks, pipes, and equipment and gives off corrosive gases as it decays. Crap is much easier stuff to handle!

Anyway, septic systems are proven, cheap, old technology . How cheap? Well, where I used to live a septic system cost $2500 and close to nothing to maintain and, by comparison, a sewer hookup cost $11,000 plus $38 per month for life. But here`s the rub. Septic systems discharge a certain amount of nitrogen containing chemicals to the ground. As the systems age and as a town grows with increased densities of septic systems, eventually the nitrates build up and reach ground water where it renders the water dangerous for consumption by children. So, a septic system that might be a great idea on acreage in the country will be phased out in a city. Septic systems are sized by the occupancy load. One house of mine had a 750 gallon tank for a 3 bedroom house. For a larger project, like a hotel, this sizing may force you to go to multiple septic tanks or to some other system. Another spin on septic systems is the above ground system used where the soil is too shallow or the water table is too high for a standard tank. Perimeter walls are built and the center backfilled with soil and the septic system is placed on top. It is more expensive but basically the same technology. The outhouses in my area in the country are raised 2 feet above the ground level because of the high water table. If not. They would overflow during the rainy season.

Ok, so you are out in the country. You have surveyed your neighbors and found they are on Plan A, crap in a shallow hole in the ground or Plan B, crap in an outhouse, which has a deep hole. Both work, but are not pleasant and tend to attract insects and vermin. My country outhouse is the only place on the property that has zancudos. They are hiding from the wind and sun. I spray the hole with insecticide before use; other folks do other things, I imagine, like get bit in the butt.

So you want to do better than above. Well, first I have no idea what the legalities are here, but if you are doing anything bigger than a family residence (like a hotel) or are working in a nature preserve or other sensitive area, you will probably find out. My first suggestion would be to visit other eco –resorts and see what they did and how well it worked and what government hoops they had to jump through. Remember the 100/300 Rule—everything you do in Nicaragua will go 100% over in cost and 300% over in time!

First, a plain old septic system seems like it would be the easy fix, especially for a small project. The waste would be processed out of sight with no maintenance inputs to speak of and the final effluent would also be out of sight and odor/insect/vermin free. I would try to have the laundry room effluent go somewhere else to take some load off the main system.

Laundry water can be used fairly easily and safely for irrigation with a couple provisos: first, there should be no contact with water used to wash clothing of people sick with intestinal problems or with baby diapers. One approach is to have 2 pipes, one going to the septic system and one going to the greywater system so that you can move the washing machine discharge hose from one to the other as needed. Given the room for error here, especially where some people have not bought into the germ theory of disease, you should probably design your system so that it never goes to where there will be unauthorized human contact. In other words, your grey water should go to underground basins located where people or animals will not dig and allow the greywater to come to the surface. Detergents have salt in them so should not be used with salt-sensitive plants and the soil should be thoroughly flushed out with rain water during the rainy season, so this shouldn`t be a big problem. I would also not use it for edible plants, with the exception of trees. It seems like it would be best for ornamentals and firewood trees, just to rule out a possibility of contamination of food. Detergent also has phosphorus, a plant fertilizer, which can cause algae blooms in ponds, so keep your laundry effluent away from ponds, etc. Put it somewhere where the plants will use up the phosphorus. There is plenty of information out there for the safe use of greywater, much of it originating in the American Southwest, where some folks have been trying hard to make use of the resource while keeping the health department happy, too.

Another approach would be to look at ``constructed wetlands``. These are marsh-like environments created using plastic or cement liners covered with gravel in which plants are grown. Treated effluent from a septic tank or other system flows thru the constructed wetland where the plants use up the excess nitrogen and the exposure to sun and air also helps clean up the water. These should be fenced to keep people and animals out, but they can be a little nature reserve and a good place to bird watch. This is a comparatively new technology, but there is plenty of info out there. Wikipedia and http://wrrc.arizona.edu/publications/arroyo-newsletter/constructed-wetla... are 2 places to start.

I have heard of aerated septic tanks but I have no knowledge of same. I think I would avoid any wastewater system that requires electricity unless if were forced on me by the govmint. Municipal plants often use facultative ponds—ponds that have the top layer of water aerated by pumps or mixers. This helps keep the odors down while not using as much machinery and electricity as would be needed to aerate the whole pond.

What about use of treated effluent for such things as watering lawns? Doable, but you are going to have to have a very well treated effluent that is finished off by treating with chlorine or UV light (more electricity) and you will then have to deal with the ``squeamish factor`` when dealing with the public. To me, it would be better to just use the effluent where there is not direct public contact and preferably delivered underground.

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For the reserves

MARENA now requires biofilter systems in the reserves where the word require has the typical meaning. For example, there are lots of new latrinas in the Tisey reserve thanks to NGOs even though, in theory, they are illegal.

Biofilter systems are basically aerobic systems vs. the anerobic septic system. I have one such system designed but never implemented.

For small projects, self-contained composting systems would be a realistic alternative. Unfortunately, I have not been able to get an official okay on such systems. The biggest negative is that they tend to either be large or require electricity to operate.

This guy, Nate, was composting human waste 6 years ago


I know because I got a buck a night off the bunk rate by carrying the pails out to the site! The things we used to do eh?

He may have been under the radar but he may be worth adding to your contact list.


represent a broad category of systems. http://en.wikipedia.org/wiki/Biofilter and other online sources hace plenty of info . I have seen 2 eco-projects here that had composting toilets. Neither was particularly pleasant to use, and in one the owner commented they were quite labor intensive, especially during peak usage. This is probably not necessary as I used one in a campground in the US desert. I think the difference was a small fan that kept the air moving and which was run by a solar system. Moving some air in a composting system is cheaper than aerating the liquid in an extended aeration plant.

Biofilters are the way to go as they use less energy, fewer moving parts, etc. The trick will be to get regulatory approval. With time some standard designs should get accepted. If the struggle to get greywater legal in the US southwest is any example, it could be a matter of decades which does not bode well for projects theat are required to use biofilter technology.

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand

Aerated septic tanks..

I looked this up out of curiosity. The new ones look like what we used to call a ``package plant``, a wastewater plant that was delivered by truck and set in place by crane. These were used in new housing tracts, hotels, campgrounds, etc, often as a stop-gap measure until sewers were available, but in sdome remote locations they could be permanent. Hook up the pipes and wires and fire it up and within 2 weeks the bugs should mature and you have a functioning wastewater plant with a discharge that will meet your permit.

The other type I saw was an add-on setup for an existing septic system, which seemed to be an emergency thing for a failed system on a difficult site.

One site estimated that compared to a standard septic system, an aerated one would cost 2 to 3 times the money to purchase, plus the maintenance and electricity. Another site estimated 1 to 8 kilowatt hours of electricity per day to run the system.

It all seems doable, and may be one way to get permissions in a reserve or other sensitive location. If I were out in the boonies far enough and there were no regulatory issues, I would be tempted to look at a standard septic system feeding to a fenced constructed wetlands and skip the mechanics and electricity.

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand


does not have to be a big, high tech deal on a small project. If your can avoid chlorinating your final effluent, fine, but if not you can finish off your water fairly easily.

The first little wastewater plant I worked at, which was running only about 10,000 gallons a day, came with a gas chlorination system but the senior operator chose not to go through the training and liabilties of using it for only 10,000gpd. So, I drilled a bunch of holes in a 5 gallon bucket and hung it below the outfall of the plant and put a few 3 inch pool tabs in the bucket and a couple more in the bottom corners of the storeage tank that was directly below the bucket. This worked fine as long as their was a daily operator there to run a chlorine test and add tabs as needed. You only have to run a minimal CL residual in the tank, 1/2 parts per million. More is not better and just a waste of chems. If the contact time is at least 30 minutes, any measurable residual is adequate. If there is any residual at all, anything that will be killed by CL has been killed. Equipment wise, all that was needed was the bucket, pool tabs, rubber gloves, and a test kit.

Incidently, I recently ran chlorine tests on Esteli tap water. The standard is the same: 1/2 ppm at the delivery point (your faucet after running the line wide open for a minute or so to get a sample of what is in the Enecal pipes, not what has been sitting in your pipes). 1/2 ppm assures that the water that presumably left the treatment plant clean has not be contaminated enroute and to discourage things from growing in the pipe system.

On 3 days I got 0 ppm and on 3 other days I got 3ppm (swimming pool water!). This is one reason I now solarize our drinking water in 2 liter soda bottles. The UV kills germs and I now leave the bottle caps open a little in hopes that the excess CL will off gas to atmosphere. (CL is great stuff for disenfection, but is not good for human health).

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand

If You Were

to aerate then chlorine would have to be introduced after aeration, right, or it would also kill off the aerobic bacteria?

Does the chlorine have any effect on the downstream plants? How quickly does the chlorine dissipate on exposure to sunlight and open air?

Did you "boost" the aeration process with any added element (like some people put Rid-X into their septic tank)? Rid-X has a national TV ad where they encourage you to sign up for a Rid-X monthly subscription. Or, is the source of the aerobic bacteria simply the air around us?

The necessary microorganisms

The necessary microorganisms are everywhere and do not have to be introduced. Under optimum conditions they need about 2 weeks to get up to speed.

The cliche in the trade is 'the good bugs eat the bad bugs'. Give them food (organic matter), reasonable temperature (not hard here) and air (bring your checkbook, mechanic, etc.) and you will have aerobic waste water treatment, which is quicker and better smelling than anaerobic treatment. Note that in most systems the air has to be distributed evenly which requires mechanical mixers and/or a network of piping leading to air diffusers.

Chlorine is usually the last step, after the biological elements have done their work. It will kill everything that is killable by chlorine. In a permitted plant that discharges to a body of water you would also have to dechlorinate with other toxic chems to not damage the biological elements in the receiving water. A cheaper method is to put the effluent in a lined pond in the sun where the CL will offgas to the environment. In a warm sunny climate this does not take long ( a day or 2--remember you are only clhorinating to the .5 ppm/30 minute standard. More is not better) and if you are using the water for irrigation this is also your irrigation holding pond.

Netnet, an aerated waste water plant is just a babbling brook on steroids, with a generous expense account and a lust for electricity.

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand


Where do you get your water test kits? Also, have you tested for chloramine?

I just brought

a cheappy pool test kit down from the States. You might try Sinsa or a pool store in Managua. I`m not running a pool or anything sophisticated, I just want some idea of what is in my drinking water. We have several permanent leaks in the Enecal distribution system in our neighborhood, plus an occacional leak that gets fixed, so our water is more suspect than the normal suspicious water here.

Another mystery is that at the new house we have what looks like salt buildup on the shower head. Normal in most parts of the desert, but this is the first time I`ve seen it here. We must be on a different Enecal well than at the other house. I use a thin wire to clean out the holes in the shower head.

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand

Salt build-up

Might the buildup on the shower head be the result of very high calcium levels in your new water supply? I know that calcium build-up is a real problem for growers in some parts of Carazo who tap into municipal supplies?

I like this post

Very informative and difficult to sidetrack and/or turn political or compare to life in Morgan County or Thompson River but I am sure it could be done...


I laughed pretty hard after reading Juanno's reply.

Long tradition

posts on something useful or the environment get few replies, but posts on politics or crime and watch the electrons flow!

"You can avoid reality, but you cannot avoid the consequences of avoiding reality." Ayn Rand