I am using Oasis laundry detergent and notice that the ingredients include surfactants which, according to wikipedia, can contain sodium laurel sulfate which is not good for greywater. Any insight into this? I emailed them to see if they can provide more details on the ingredients.
"In the U.S., most soap and detergent manufacturers don’t list their ingredients except in very general terms: “cleansing agents,” “surfactants,” “brighteners,” “enzymes,” “perfumes” etc. — everything beyond that is a “trade secret.”
Sodium lauryl sulfate is technically a detergent; were the sulfate not there, then it would just be sodium laurate, a soap. Soaps and detergents can both be called surfactants, as they activate dirt particles on a surface to become soluble in water so that they wash away. Neither one is good for greywater, because you want biological processes going on in greywater to turn into nutrients for your plants, and both types of surfactant are anti-bacterial. Often, if you just let greywater sit around long enough, the surfactants will glom onto some dirt or minerals in the water and deposit out, and then the biological activity you want can resume. But better than waiting for the surfactants to settle out is to not let a lot of excess surfactant get dumped into the greywater tank in the first place, as in when you drain out the wash water. If your wash water is still sudsy when the wash cycle is over, then you have started off with too much soap or detergent and that is the source of your greywater problem.
It's a matter of using just enough surfactant without using too much. Another way to minimize your use of surfactant is to use soft water, like DOW chemical explains in this video:
If you have very hard water, then the greywater bacteria have little to worry about from surfactants, because little surfactant will make it through to the greywater. If you are using rainwater in your washing machine, then you probably don't have to add much surfactant, and again you are not causing much distress to the greywater. But if you have moderately hard water (like the kind described in the video) and you add excess soap or detergent to get a nice, sudsy wash, yes, that is going to be "not good" for your greywater.
One chemistry fix for this problem is to use washing soda in with your soap or detergent. Washing soda is sodium carbonate, which acts as a softening agent in with the wash water so that you can use less soap or detergent in the first place. But washing soda still contains sodium, which can be problematic for plants. If you live in an arid climate, like out west, soil sodium levels can already be high, so you don't want to be watering your plants with greywater that has sodium added. In that case, you would be better off adding ammonia to your wash water. The ammonia that is commonly sold in stores is around 5% NH4OH in water, and it does a good job of solubilizing dirt so you get a clean wash. Plus, the ammonium ion in the greywater acts as a nutrient for the bacteria and the plants that you sprinkle it on.
When I do laundry, I use a small amount of liquid detergent, maybe half of the recommended amount, and I let it sit on the pre-soak cycle for a couple of hours. That extra time makes sure that the surfactant has surfacted on my dirty clothes is not quickly rushed down the drain into the greywater. After the pre-soak sitting, I add about 1/2 cup of regular household ammonia to the wash water and then let it resume with the wash cycle. If you adopt this method, I think you will find that you are less likely to send a bunch of suds (bad) down the drain into the greywater.