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.