Treatment Systems How they work and what to consider when selecting one. Joe Walsh IOWA Conference 2015

Transcription

1 Treatment Systems How they work and what to consider when selecting one Joe Walsh IOWA Conference 2015

2 Content Treatment systems overview and certification for Irish market Types of secondary treatment systems and technologies Secondary treatment processes Practical differences in operation Site circumstances requiring extra consideration Combining with a pressure infiltration system

3 Treatment Systems Secondary treatment systems (not septic tank systems) Often called Bio systems, Biocycle systems, proprietary systems, packaged etc. Designed to provide secondary quality effluent per EPA CoP 2009

4 Types of Treatment Systems Main types Mechanical aeration systems o Processes include BAF, SBR, MBR, MBBR, RBC Media filter systems o Sand, soil, peat, bark, coir, foam... Constructed wetlands/reed beds o Horizontal, vertical

5 Certification Systems must be tested and certified to meet CoP and SR66 (BOD20/TSS 30/NH4 20) CE marking indicates systems have been tested, not that they are suitable. Systems must be certified under EN or EN to meet Irish standards.

6 List of Irish Certified Systems

7 Treatment Categories Three categories of treatment Primary (solids settlement + filtering) Secondary (BOD/TSS/nitrification) Tertiary (N, P, disinfection) Most secondary systems include primary and secondary treatment Some provide tertiary treatment of some parameters

8 Treatment Process Secondary treatment process is different from an anaerobic septic tank that has no oxygen ST system relies on the soil to be aerated to provide treatment Secondary systems treat the raw sewage influent before release to the environment Requires an Aerobic process via aerobic microbes Two main processes used for treatment Suspended growth no media is used Fixed film/attached growth biomass attached to media Both have advantages and disadvantages

9 Ideal conditions for Aerobic Microbes Sufficient Oxygen Nutrients(food source) Stable ph Moisture Stable temperature Solid surface (media) to attach to. Treatment is most stable when the biomass population has a consistent food supply.

10 Ideal conditions for Aerobic Microbes Sufficient Oxygen Nutrients(food source) Stable ph Moisture Stable temperature Solid surface(media) to attach to. Treatment is most stable when the biomass population has a consistent food supply

11 Types of Treatment Systems Main types Mechanical aeration systems o Processes include BAF, SBR, MBR, MBBR, RBC Media filter systems o Sand, soil, peat, bark, coir, foam... Constructed wetlands/reed beds o Horizontal, vertical

12 Mechanical Aeration Systems 1. Fixed film /attached growth with fixed or loose media (MBBR). 2. Media filter systems (also fixed film) 3. Suspended growth systems with no media Primary tank is usually built into small systems but can be separate. Volume of the primary tank affects the desludging frequency. A septic tank upstream can provide extra primary capacity but may affect Irish compliance

13 Treatment Processes Fixed Film Fixed Film/attached growth Treatment process is usually more stable than suspended growth. Media volume is based on BOD loads in domestic effluent. Continuous flow, so treatment is affected by home usage pattern. Process can be adapted to achieve some tertiary treatment. Loose media may be removed during desludging by tanker.

14 Biological/Submerged Aerated Filters (BAF/SAF) Fixed film treatment process with submerged media Three chamber system Process may be adapted to achieve some tertiary treatment (N and P) Usually little bacterial treatment w/o UV Some systems can be adapted for seasonal use by recirculating effluent to keep microbes alive.

15 Rotating Biological Contactor (RBC) Fixed film treatment process Motor controlled disc rotation Three chamber process Air supplied as partially submerged discs rotate above water level

16 Treatment Processes Mechanical Aeration Suspended Growth Continuous flow operation. Process used for large scale treatment systems. Sensitive to influent variability Often have high populations of organisms. Usually little bacterial treatment w/o UV Not well suited to seasonal use as microbes will die off unless modified by the manufacturer.

17 Treatment Processes Mechanical Aeration Sequential Batch Reactor (SBR) Processes influent in 3-4 batches/day 4 stage process (fill, react/aerate, settle, discharge) Evens out influent variability (vol and strength) Process may be adapted to achieve some tertiary treatment (N and P) Usually little bacterial treatment w/o UV Some systems can be adapted for seasonal use by recirculating effluent to keep microbes alive.

18 Sequential Batch Reactors (SBR) Processes influent in 3-4 batches/day 4 stage process (fill, react/aerate, settle, discharge)

19 Membrane Bioreactor (MBR) Membrane barrier screens effluent High MLSS and bacteria provides treatment High level of treatment is possible Very sensitive process and high maintenance

20 Treatment Processes Media Filters Media Filters and Constructed Wetlands Usually requires a large area Treatment process is usually more stable Process cannot be adapted to achieve some tertiary treatment w/o recirculation Air supply can be inconsistent e.g. due to cover material Can become saturated due to high water table flooding Can be clogged at the surface by grease or high strength influent Often high bacterial removal from effluent Short start up period so well suited to seasonal use

21 Domestic Wastewater per EPA CoP

22 Treatment for Sensitive Areas And remember not all onsite systems involve Domestic wastewater.

23 Examples of Site circumstances requiring Extra Design Consideration Factors Free draining soils (sand, gravel) Shallow soils over bedrock/sinkholes/fissures Holiday homes Concerns Little soil treatment (mainly pathogens) Little soil treatment (mainly pathogens) Periods of inactivity Nursing homes, crèches, Medication/high strength restaurants etc. influent/fog Event venues/racecourses etc. Flow variability Remote/elevated infiltration areas Pump selection/rising main diameter selection

24 How to deal with Design Challenges Select a Treatment Train to suit the site and environment Specific treatment systems (+pre-treatment/tertiary) with soil infiltration systems that maximise soil treatment If a pressure system is included check: Site TDH incl pressure losses in rising main and pipe network The pump specification is suitable (head and flow) Dimensions of pump tank to provide the dose volume Designs for Planning purposes only should not be permitted This requires site specific designs and Local Authority review of site specific designs AND careful consideration of any design changes.

25 Combining a Treatment System with a Pressure Infiltration System Pipe network suppliers should supply the pump and dose volume required to pressurise the network. Pump and dose details are specific to each pipe network. The pump must be selected based on the site TDH head to function - i.e. elevation and pressure losses. Many systems pump < 40 L/dose not enough to fill the pipe network Often a different pump or separate pump tank is necessary.

26 Monitoring and Maintenance All treatment systems need monitoring and maintenance All infiltration systems need monitoring and maintenance Systems should be designed so that maintenance is easily done. Regular attention can prevent a major replacement.