PURIFYING WATER FOR COMPOST TEA
Q: Our water treatment plant is preparing to switch disinfecting chemicals, from chlorine to chloramines. What are the differences between the two chemicals? We make a lot of compost tea each week. How will chloramines affect the microbes we are trying to grow in the tea? We have found that we can remove the chlorine by aerating the water. Our chlorine readings were reduced from 0.85 to 0.05 ppm after six hours and 0.00 ppm by the next morning (21 hours) with constant aeration. Is there any way to similarly reduce the presence of chloramines in water?
A: Unfortunately, you are likely be affected by your water provider's switch from chlorine to chloramine. Both chemicals are disinfectants, intended to kill bacteria, which you want to preserve in compost tea. However, chloramine lasts longer in the water than chlorine does and it cannot be removed by aeration. Be prepared to add one or more steps to treat the water that you use to make compost tea, in case you find that chloramine does impair the microbial population of the tea.
Chlorine has been, and remains, the most common chemical used for disinfecting water supplies. The chlorine added to water is a strong oxidant. It is very reactive and unstable. Chlorine quickly tends to form chlorine gas, which dissipates from the water. This is why residual chlorine can be reduced and even eliminated by allowing an open container of the water to sit for a time. Boiling, stirring or aerating the water hastens the loss of the chlorine gas, as you have discovered. Unlike chlorine, chloramine does not quickly dissipate from water. Your aeration strategy will not reduce the chloramine level to a great extent.
Chloramine is a combination of chlorine and ammonia. It is much more stable, i.e. longer lasting, than chlorine so it can be a more effective disinfectant over time and distance in the water distribution system. Chloramine is less reactive than chlorine. For instance, it does not form chlorinated by-products, such as trihalomethanes (THM), which are suspected carcinogens that form by a reaction between chlorine and organic substances in the water. Chloramine also can improve water quality in cases where chlorine reacts with compounds that impart a bad taste. These are among the reasons that water treatment facilities are considering switching to chloramine disinfection.
Generally, water with residual chloramine is safe to drink and to use for bathing, cleaning, irrigation, etc. However, there are a few uses that are detrimentally affected, depending on the residual levels. Chlorine and ammonia, and therefore chloramine, are toxic to fish and amphibians (passes through the gills and into the bloodstream and reduces the blood's oxygen carrying capacity). Also, water with chloramine cannot be used for kidney dialysis (also causes loss of the blood oxygen capacity). Chloramine can impact a few other processes that require nearly pure water, such as laboratories, computer chip manufacturing, beverage producers and biotechnology firms. These sensitive water users require point-of-use treatment methods such as neutralizing chemicals and/or special water filters.
Since chloramine is a disinfectant, it might significantly harm processes and products that rely on microorganisms. Compost tea certainly falls into this category. However, as usual, it's the dose that makes the difference. The San Francisco Water Department, which will switch to disinfecting with chloramine in February 2004, expects residual chloramine concentrations in the range of two to four mg/liter, with an ammonia to chlorine ratio of 5:1. Is this concentration high enough to spoil the compost tea? There's no available data to make a judgement from the concentration alone. Probably, the best way to determine whether the tea will be affected is by experiment and testing. Vicki Bess, with BBC Laboratories, says "we can test the compost tea to characterize the microbial population. However, to determine whether the chloramine is having an effect, we need something to compare the results to - a test of compost tea that was made from chloramine-free water." It might be a good idea to have the compost tea tested before the switch to chloramine is made and then again after the chloraminated water begins to flow.
If you find that the chloramine in the water is detrimental to the tea, there are several options to remove it. The larger concern is the chlorine. Aquarium and pond supply outlets offer chemical products that dechlorinate water, and they will work with chloramine. Most of these products use sodium thiosulfate (Na^sub 2^S^sub 2^O^sub 3^), which reacts very rapidly to neutralize the chlorine (calcium thiosulfate can also be used). With chloramine, what remains after dechlorination is the ammonia, which is a problem with aquariums and fish ponds since ammonia is toxic to fish. So, in fishy circumstances, the residual ammonia must be removed with additional chemicals or filters, such as a biological filter or zeolite. However, the ammonia is probably not a problem for the microbes in compost tea. While it conceivably might alter the microbial character, it should not be toxic at the residual concentrations found in water supplies. Therefore, dechlorination with chemicals such as sodium thiosulfate is probably sufficient.
Water filters are another option for removing chloramine in water supplies. Although household activated carbon filters can remove chlorine, the ammonia in the chloramine interferes with the process. Therefore, a catalytic activated carbon filter is necessary. The catalyst breaks the ammonia chlorine link and the filter adsorbs the chlorine. The ammonia passes through the filter with the water. If necessary, the ammonia can be captured with a second absorbent like zeolite. One problem with carbon filters is that they require a relatively long contact period to adsorb the chlorine. You may find the treatment to be slow or the size of the filter to be large. In addition, the activated carbon will need to be replaced periodically (as will zeolite).
In summary, the bad news is that the switch to chloramine is likely to create a few headaches for the compost tea production system. The good news is that there are options for correcting it. It is a good idea to consult your water provider and/or a water treatment professional for information and advice on treatment techniques for removing residual chloramine from the water.
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Robert Rynk/ Q&A
BioCycle
419 State Ave.
Emmaus, PA 18049
fax: 610-967-1345
email: biocycle@jgpress.com
[Author Affiliation]
Robert Rynk/ Q&A
BioCycle
419 State Ave.
Emmaus, PA 18049
fax: 610-967-1345
email: biocycle@jgpress.com
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