UKTC Archive

RE: Biodisc effluent - impact to trees?

Subject: RE: Biodisc effluent - impact to trees?
From: Igoea, Andrew
Date: Dec 22 2017 09:04:26
Thanks for all the responses to this.

To clarify, its treated effluent entering the soil through a soak away type 
of arrangement rather the application raw sewage to the surface.

To summarise:
- Tree species have a natural range of soil conditions which they are suited 
- The trees on this site will have grown and adapted to the soil conditions 
present and will be able to cope with natural variations in soil moisture, pH 
and other soil properties.
- The question is whether the effluent will create conditions beyond the 
range that the trees can cope with
- The anhydrous ammonia is likely to increase the levels of N in the soil and 
lower the soil pH
- The quantity of effluent entering the soil will increase the soil moisture 
content and may lead to anaerobic conditions.
- All these changes to soil properties could impact fungi, soil microbiology 
and fauna
- The impact to fungi includes a potentially detrimental impact to 
mycorrhizal fungi associations, key to tree health.
- Anaerobic soil conditions could lead to root dieback, leading to crown 
dieback, leading to safety concerns and an impact to amenity value.
- Root dieback and decay, resulting in degradation of tensile strength in 
structural roots could lead to an increased risk of uprooting
- Increased soil moisture could also increase the risk of uprooting to due to 
the reduced shear strength of soils around/beneath the root plate

Anything else??

-----Original Message-----
[] On Behalf Of Igoea, Andrew
Sent: 21 December 2017 10:20
To: UK Tree Care
Subject: Biodisc effluent - impact to trees?

Hi All,

Has anyone had experience with assessing the impact of discharging biodisc 
effluent (treated sewage) into the rooting zone of trees?

The treated effluent will contain 10mg/L suspended solids and 3.8mg/L 
ammonia, and will have a BOD of 10mg/L. The output could be between 1-2 cubic 
metres per day.

The treatment facility is at the top of a steep bank and the trees are below 

I know the proposal will impact the moisture content and chemical composition 
of the soil, which could impact the mycorrhizal associations and soil fauna, 
but will it have a significant detrimental impact on the trees?


Andrew Igoea  | Arboricultural Officer
Forestry, Amenity and Lands Directorate | Department of Environment, Food and 
Thie Slieau Whallian | Foxdale Road | St Johns | Isle of Man | IM4 3AS
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