Plan-It STOAT: Wastewater Treatment Plant Design Tool

Dynamic prediction modelling tool for the selecting, sizing, and siting of wastewater treatment works (WwTW).

Looking for STOAT: Wastewater Works Modelling?

Jeremy Dudley is our expert in Plan-It STOAT

Get in touch Get in touch

Optimised WwTW design

Wastewater treatment plant modelling software is now widely used to simulate more effective operations (see WRc's STOAT). However, current methods for initial implementation or design of WwTW (such as manual or spreadsheet calculation) are neither cost- nor time-effective, and lack efficient planning of effluent water quality, cost, land area, and available hydraulic grade. 

In collaboration with major US company CDM, WRc provides the tool to evaluate the construction, expansion, and modification of wastewater treatment facilities both rapidly and economically. The user inputs criteria and parameters relating to water quality and facility features, and Plan-It STOAT will quickly evaluate preliminary treatment plant designs, including sizing the unit processes; evaluating performance, major design constraints, the footprint for the facilities, and preparing a preliminary hydraulic profile through the treatment process.

Supportive user experience

Our models allow for simplified use and increased computational speed, facilitating the comfortable development of expertise in advanced design methods.

Fully integrated output files

All three technical disciplines - hydraulic design, process engineering and cost estimating - are able to share information, more effectively coordinating multi-discipline design efforts.

Updated and improved V1.2

Constantly evolving, Plan-It STOAT now includes new variants for activated sludge and anaerobic digestion models, as well as improvements to stability, cost functions, user-written models, and support documentation.

Example applications

See below how the positive intervention of Plan-It STOAT might have predicted hypothetical site issues.

  • Hydraulic constraints
  • Footprint issues
  • Cost comparisons

When designing according to assumptions about tank volumes and so on, changes may seem small compared to the effortful recalculation of grade lines. 

Failing to recheck the hydraulics may result in the commissioned site not accepting the required peak flow, if water levels exceed the channel depth.

Plan-IT STOAT software allows rapid recalculation of the hydraulic grade line, preventing optimistic evaluations of true process limits.

When weighing up options for increasing treatment capacity, cost-based decisions (e.g., installing extra settling tanks), without considering alternative site layouts, can be detrimental. 

Failing to ensure sufficient land around the location of extra tanks could result in unforeseen headaches (e.g., additional pumping costs to the adequate location).

If foreseen and designed using the Plan-IT STOAT 'buffer zone' tool, footprint-related issues would have influenced the original decisions to increase treatment capacity.

When designing the operations used at WwTW, it is important to consider how capital vs operating cost trade-offs could make or break decisions.

More cost-effective choices can be missed by failing to evaluate assumptions about the relative inflation of energy costs, labour required for operation and maintenance, and the replacement frequency for mechanical equipment.

Using Net Present Cost (NPC) calculations allows Plan-It STOAT to reconcile differences between processes such as trickling filters and activated sludge, or anaerobic digestion with pre-pasteurisation and TAD.


Ensure optimum design for your WwTW and safeguard the future, now. 

Enquire with our experts about how Plan-It STOAT can help you via the form at the bottom of this page.

Functions and benefits

Consisting of interrelated ‘process’, ‘hydraulic’ and ‘site layout’ functional modes, Plan-It STOAT will help an experienced designer to carry out:

Performance evaluations

Flow and mass balance calculations

Preliminary process calculations

  • Input based on either unit process sizes, or influent loads and effluent water quality.

Preliminary hydraulic calculations, covering:

  • Head losses for a range of common fittings.
  • Flow splits and unions.
  • Open channel flow, including automatic recognition of flow patterns and appropriate method selection of calculating the grade line.

    Capital and operating cost comparisons of alternatives

    • Estimates capital and annual planning level costs (including power, chemical and labour) using TR 61 (UK) and CDM’s data (US).
    • Allows for regional (or other) cost conversions.
    • Provides Net Present Cost (NPC) comparison between high/ low capital/ operating cost design alternatives.

    Site planning

    • Units are represented by geometric shapes which can be rotated and moved on an interactive flowsheet.
    • Importing existing site maps (including CAD drawings) or aerial photographs (with visual feedback of buildings and roads) can facilitate site layout.
    • ‘Buffer zones’ can be placed as needed to allow consideration of site access and equipment installation.

    STOAT: Wastewater Plant Modelling

    The first choice for dynamic simulation of wastewater treatment plant performance, available as Freeware.

    Start optimising and troubleshooting your WWTW operations.

    Read more

    Related services

    Created by potrace 1.16, written by Peter Selinger 2001-2019
    Full name
    Email address
    Company name
    How can we help?

    Can we stay in touch?

    Your details will be stored within our CRM to allow us to handle your enquiry. We'd love to keep in touch and send you our newsletters and other notifications we think may be of interest to you. Please let us know if we have your permission for this.

    Full name
    Company name
    Email address
    Phone number

    Can we stay in touch?

    Your details will be stored within our CRM to allow us to handle your enquiry. We'd love to keep in touch and send you our newsletters and other notifications we think may be of interest to you. Please let us know if we have your permission for this.

    Jeremy Dudley

    Consultant Engineer (Treatment Processes)

    Jeremy's expertise lies in the modelling of sewage treatment systems; activated sludge systems; and modelling of processes and hydraulics at sewage and industrial effluent treatment works, both in the UK and overseas. He is the lead developer of WRc's dynamic wastewater modelling tool (STOAT) as well as the steady-state design version of STOAT (Plan-It STOAT). He is also involved in the development of WRc's cost and carbon modelling software (TR61).