Question:What are some observable tell-tale signs of wastewater pollution?

by bhamster | July 28, 2021 21:01 | #27373

This could be for wastewater from different sources---domestic and municipal, industrial, agricultural, stormwater...

What are some of the first clues that might indicate wastewater pollution in a water body?


@jesseslone Thanks for coming by Open Call yesterday! I'm wondering if you have any thoughts about this question? You mentioning that treated wastewater with anything other than a slight earthy smell indicates something is off was informative.

Is this a question? Click here to post it to the Questions page.

Reply to this comment...

Yes, properly treated wastewater should ideally smell like a forrest stream... clean and possibly a little earthy. Also, I should note that my expertise is in organic wastewater. I don't know much about treating wastewater from industrial plants, except food processing plants.

That being said, here are some indicators that are visible in the discharge area:

A sickeningly sweet smell: The plant is septic (no oxygen) and the result is carbohydrate chains that smell sweet in the effluent (discharge water).

Milky or light grey or brown discharge (high turbidity): Under-treated wastewater. Residential or Municipal wastewater is often just a light brown or grey color. In the treatment plant, bacterial colonies (flock) should capture these suspended solids, if they aren't, there's either too much flow for capacity (common in surges), or the bacterial microbiome in the treatment reactors is not healthy.

Rotten egg smell: This is also under-treated wastewater that has a high concentration of hydrogen sulphide producing bacteria. Most commonly associated with sewer collection systems and pump stations, it is due to the way that biofilms in the pipes develop when there is insufficient oxygen in the sewer to promote aerobic biofilms. The ebb and flow of water usage cycles provides the ideal environment to form the biofilm.

Lots of green algae growing on the surfaces around the discharge: Not necessarily a bad thing, it just indicates the presence of nitrate and nitrite in the wastewater. The problem with higher levels of nitrogen in the discharge is that it can cause "bloom" events which can starve the receiving waters of enough oxygen for fish and other aquatic life.

Dark brown to black mud around the discharge area: This is an indication that wastewater biosolids are coming out in the effluent. This can happen due to surges, insufficient biosolid removal (often called sludge wasting), or poor settling in the clarifier (the part of the plant that separates bacterial flock from the treated water so that the bacteria can be recycled).

Perhaps we could work up some sort of visual decision tree to help diagnose why treatment plants are underperforming? I'm still trying to figure out ways to help operators and community members work together for the good of receiving waters.

Is this a question? Click here to post it to the Questions page.

This is incredibly helpful, thank you! Some kind of visual to help diagnose treatment plant issues would be great. Maybe we can start brainstorming on an upcoming call?

Is this a question? Click here to post it to the Questions page.

Hi @jesseslone , this comment is to translate your answer that I consider very valuable. If it does not seem appropriate, I remove it:


Las aguas residuales debidamente tratadas deberían oler idealmente como un arroyo forestal ... limpias y posiblemente un poco terrosas. Además, debo señalar que mi experiencia está en aguas residuales orgánicas. No sé mucho sobre el tratamiento de aguas residuales de plantas industriales, excepto las plantas de procesamiento de alimentos.

Dicho esto, aquí hay algunos indicadores que son visibles en el área de descarga:

Un olor repugnantemente dulce: la planta es séptica (sin oxígeno) y el resultado son cadenas de carbohidratos que huelen dulcemente en el efluente (agua de descarga).

Descarga lechosa o de color gris claro o marrón (alta turbidez): Aguas residuales poco tratadas. Las aguas residuales residenciales o municipales suelen tener un color marrón claro o gris. En la planta de tratamiento, las colonias bacterianas (flóculo) deben capturar estos sólidos suspendidos; si no lo hacen, hay demasiado carga para la capacidad o el microbioma bacteriano en los reactores de tratamiento no es saludable.

Olor a huevo podrido: también se trata de aguas residuales poco tratadas que tienen una alta concentración de bacterias productoras de sulfuro de hidrógeno. Más comúnmente asociado con los sistemas de recolección de alcantarillado y las estaciones de bombeo, se debe a la forma en que se desarrollan las biopelículas en las tuberías cuando no hay suficiente oxígeno en el alcantarillado para promover las biopelículas aeróbicas. El flujo y reflujo de los ciclos de uso del agua proporciona el entorno ideal para formar el biofilm.

Muchas algas verdes crecen en las superficies alrededor de la descarga: no necesariamente es algo malo, solo indica la presencia de nitrato y nitrito en las aguas residuales. El problema con los niveles más altos de nitrógeno en la descarga es que puede causar eventos de "floración" que pueden privar a las aguas receptoras de suficiente oxígeno para los peces y otras formas de vida acuática.

Lodo de color marrón oscuro a negro alrededor del área de descarga: esto es una indicación de que los biosólidos de las aguas residuales están saliendo en el efluente. Esto puede suceder debido a sobretensiones, eliminación insuficiente de biosólidos (a menudo llamado desperdicio de lodos) o sedimentación deficiente en el clarificador (la parte de la planta que separa el lote de bacterias del agua tratada para que las bacterias puedan reciclarse).

¿Quizás podríamos elaborar algún tipo de árbol de decisiones visuales para ayudar a diagnosticar por qué las plantas de tratamiento tienen un rendimiento inferior? Todavía estoy tratando de encontrar formas de ayudar a los operadores y miembros de la comunidad a trabajar juntos por el bien de recibir aguas.

Is this a question? Click here to post it to the Questions page.

Reply to this comment...

One additional note about algae formation. It's not uncommon to have high algae formation even in untouched waters. I have been backpacking in Colorado to lakes where there are no human settlements upstream and the entire bottom of the visible portion of the lake was algae biofilm, as well as the stream exiting the lakes for probably a half mile was also covered in biofilm anywhere the water was slow moving. The area was only accessible by foot or horseback and was about five miles upstream from the nearest building or road.

I wondered how there could be enough nitrogen to support it, I can only assume that the percolation through the soil must carry sufficient nitrogen to supply the algae or that there are sufficient nitrogen fixing bacteria in the biofilm.

Reply to this comment...

Some very good points! Thank you for the information. My major concern around northern Ohio has always been nitrate run off from fertilizers. Fertilizers are absolutely essential, no doubt about it. But so is drinking water. The state has limited times when farmers can fertilize the soil. But still, the run off of nitrates in lake Erie has caused growth of bad bacteria. This has mostly been in the Toledo area, but it has gotten worse and is working it's way east. Some water intakes have been closed to slow the spread. Detection? There are several possible different ways. There are low cost test papers, ion selective electrodes ( modified pH meters), and satellites. The nitrates cause the growth of a bacteria that grows a weird shade of green, allowing visible detection by satellite. And that's just for starters.

Is this a question? Click here to post it to the Questions page.

Yikes, sorry to hear about this @Ag8n. What's enabling the problem to spread east?

Visible detection with satellite imagery is exactly the kind of thing I'd like to look more into--thank you for the suggestions!

Is this a question? Click here to post it to the Questions page.

@Ag8n I think part of the answer to fertilizer might be efficient recycling of wastewater and the treatment byproducts, like biosolids. For example, the current best practice is to convert ammonia, nitrate, and nitrite in wastewater into N2 and off-gas it back into the atmosphere so that it doesn't cause algae blooms. Obviously capturing it and using it on crops would also keep it out of the water. It's sort of like the inverse of food miles. Some worry about how far the food travels, but then another concern might be where we concentrate all of nutrients that were used to grow that food. There is the added challenge of getting them recycled and back to the places where the food is grown so that they don't create negative side effects in watersheds that people rely on.

Another issue is pollutants that there are no good processes to treat, chemicals that don't break down, like PFOAs and such. These are an impediment to recycling wastewater to grow food crops because they are absorbed by the plants.

Reply to this comment...

It was believed to be high level of nitrates, although maybe the time applied and amount applied has a major part in it, too. To be honest, I think more work needs done, both now and in the future. Water demand and food demand will both increase. And the total reason for the problem doesn't seem to have been identified. As for the satellite, you maybe able to use an RTLSDR , with a fair number of accessories ( low noise amps, stuff like that) to receive the signal. That's as long as the satellite signal is in the 24 Mhz to 1800 MHz range. There are converters that could downconvert a higher frequency signal. But generally, at higher frequencies, you may have bandwidth problems. The draft has a max bandwidth of about 2 Mhz. Maybe a little more, if you are lucky. Then software could be an issue. Although there is already a lot of freeware for many satellites.

Reply to this comment...

Another answer to the original question from someone at 500 Women Scientists, with experience in microbiology:

"I don’t know if there is a single catch-all answer but usual signs are things like significant drops in the dissolved oxygen concentration or if you know where an inlet is you might visibly see a significant change in the color or turbidity upstream vs downstream. Sometimes algal blooms are signs but that could be runoff from farmlands or other places with higher nutrients supplied to streams.

The slightly cheaper than a full lab-scale study but still kinda expensive would be to do some microbial community composition sequencing on a minion nanopore… it’s a kinda portable sequencing device and if you do something like 16S rRNA amplicon sequencing and combine it with something like SourceTracker software it might pickup higher loads of influent/untreated wastewater…"

Reply to this comment...

Wow! How interesting all the information generated from a question! Congratulations @bhamster for the excellent question. I congratulate everyone who responded for the information shared! There is a lot to work on, investigate and apply!

Reply to this comment...

Log in to comment