yes is possible the phenomenon is called self purification of natural stream you may check the attach article
Agree that some potential exists, but its potential may depend on factors as suggested by Dr. Musa. But dilution mentioned in above reference is not necessarily purification, it is just altering of concentration by adding water, but pollutant load may be same. In some streams, a portion or perhaps in some instances of particular contaminants such as those adhering to sediments, a substantial amount of filtering can occur within the streambed or hyporheic zone that filters at various rates according to the substrates and pressure head and removes some contaminants. This filtering can provide some detention or residence time for biological breakup, etc. Not necessarily every contaminant or pollutant can be filtered or breakdown purified per se, as some may deposit in the substrate, such as Hg is heavy and may settle and remain, potentially entering groundwater. Most agencies that address point source discharges are not going to consider the full potential of natural stream purification, in part because this can vary with the situation, pollutant, substrate, gradient, discharge, etc. For the Hg mentioned, it is no more desired to have it settle in the streambed or accumulate on the bedrock as we know that ionic Hg can be converted to methyl mercury under anerobic conditions such as wetlands that are likely to exist in the deep substrates of streambed. In many instances, it is just going to make sense to remove at least what can be easily removed as well as toxics or excessive nutrients before discharging to waters.
An old saying that "the solution to pollution is dilution", was a catchy saying, has never been true. But by some years back, it was believed that one of the beneficial uses of streams was to remove human and solid wastes, dump in stream and it may disappear in next flood, with lack of understanding or consideration for the downstream implications. Likewise, I think one would find that if streams could self purify waste waters, water quality from point and non-point sources would not be an important issue. In many countries, water quality laws and BMPs have been found to be needed to protect the public and aquatic resources from the negative effects as the difficulty of cleaning up polluted waters is much greater than prevention or treatment, so the waters can be safely used for many beneficial uses. Even though there may be some degree of self purification and biological breakdown, we cannot count on them as being sufficient.
YES. the pollution level goes down with time and distance of flow.
you can find examples from http://enpho.org/ by contacting them if not available in web page.
They have long term data for Bagmati River in Nepal.
Dear Mr.Hansen, you are perfectly right. But Hg is a heavy metal which results from Industrial wastes not Sanitary wastes (Municipal wastewater ) .So is the case for Cr, Cd, Se, Ba, .... and other heavy metals which can not treated by ordinary treatment processes like dilution. BOD ,COD can be treated by dilution. Many thanks for your special attention. Sincerely yours
Yes is possible, but it depends of the water flow and oxygen injection due by the water contact with rocks and stones. The slope of the river also is very important to remove the nutrients.
Yes, I agree your response on Hg was a poor example as not typically present in sanitary wastewater. My poorly illustrated point was meant to illustrate that when pollutants are discharged into streams, control is lost and has potential to effect downstream surface and subsurface waters increases. I did not mention, but areas with loosing streams may have both greater filtration and bioremediation, but also greater potential impacts to groundwaters if the self purifying mechanisms are not effective. Effects can also depend on conditions, such as if downstream stream reach(s) from excessive sediment accumulations were a braided stream with high water tables, poorly drained hydric soils and frequent flooding, the area with the added wastewaters may detain and filter, but may also become a swampy, public health hazard.
I don't have the design details or specs, but a three pond detention/retention system before discharge can be very useful to help remove sewage solids, offer some breakdown period (added aeration if needed) before discharging and was used at a popular state park in Missouri where we conducted some research for additional pre-filtering and nutrient removal potential before discharge to trout waters with popular fishing. If interested, this co-authored paper 1975 was put into researchgate.
The effects of any individual proposal are apt to vary substantially with the wastes and conditions, and at times and places in the past, the effects of pollution were considered, "out of sight, out if mind". This topic continues to be an area where informed treatment options may be identified by professionals with an estimate of their individual effects prior to decisions. There remains opportunity for monitoring and research to address the effects of sanitary wastewater discharges as well as affordable wastewater treatment and removal options that reduce effects approaching or to acceptable levels. Since quality water is a requirement for life and health, and has many beneficial uses, each society or country must decide the degree they wish to consider or regulate this issue.
Fecal coliform pulses of exceptional high concentration associated with infrequent stormwater overload, leakage and discharge of a community sewer line system were found many miles downstream at high concentrations and after much dilution (brief report in researchgate, ~1998).
Special thanks to your attention. As regards effluent discharge standards which depend on stream flow , it was (60 ppm BOD5) , (40 ppm SS).Nowadays it is (30), (20)consecutively , due to the the reduction of stream flow of Tigris and Euphrates, resulting from dams construction at the upstream built by Turkey and Syria. I'm totally grateful for your valuable information and knowledge.
Yes, if you need an example, the Grand River in Southern Ontario receives a relatively high amount of sewage discharge, and while there is some inherent recovery, a significant improvement in water quality occurs due to groundwater recharge. So dilution of surfacewater contaminated by sewage discharges (treated) with clean groundwater
Concentration of pollutants in surface sources thins out downstream when looking at it from the source point. However, the level of such concentration may not be as viewed because surface water is highly susceptible to contaminants and this may be introduced at any point along the river channel. Thus, such concentration may become more concentrated or thins out depending on the events of pollutant introduction along the channel. Thus there is need for spatial and temporal water quality assessment along the stream to ascertain the quality status of such river water. The processes of self purification in soil water is not as in surface water.
Yes , Pollution level may decreases with dilution. This can be examined by chemical analysis.
Yes, I agree the responses of both Nabeel Al-Saati and Hansen.
But effluent discharge standards are vary from country to country too..
Self purification after some distance on a flowing river is possible for any given pollutants involved. However, further distance on the river may introduce additional pollutants which may be the same as the previous ones or entirely different. Dilution may reduce the composition along a flowing river. Analysis may be required to determine the trend of such purification/pollution in a given reach of the river and how new pollutants are introduced.
Yes is very possible : The self purification of natural water systems is a complex process that often involves physical, chemical, and biological processes working simultaneously.
I Agree with the idea that river is able to purify itself because a good treatment for pollution is dilute it. By continuous flow of river water.
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