System Analysis and Monitoring

is a problem-solving technique that allows the description, understanding and analysis of environmental compartments (systems) and their processes

System: is a set of interrelated objects (elements, parts) that fulfill a certain function

-> systems can be natural or artificial (man-made)

System purpose: The system fulfills a certain function, i.e. it can be defined and recognized depending on the systems nature. For example, system activated sludge process -> biological wastewater treatment

System structure: The system has a characterisitc constellation of system elements that interact between each other to determine its function, purpose and identity. For example, system elements activated sludge process -> Aeration tank, secondary settling tank, …

System identity: A system loses its identity if its integrity is destroyed. A system therefore not divisible, i.e. the system purpose can no longer be fulfilled if one or several elements are removed

System boundaries depend on the purpose of the system description

Coupling to the environment is much weaker than the internal coupling in the system

Existing couplings to the environment are not functionally relevant

Inputs are not significantly affected by the system itself or by feedback of system output

Describe completely the actual system state

Unit of measurement is not clearly defined (e.g. storage in reservoir -> Volume in m3, water level in m, rainfall in mm)

State variables cannot be computed directly from other known quantites n the system or its environment

Numer of state variables -> dimension of the system

Know about the past system behavior; recording variables, not processes

RElated to exogenous influences on the system and feedback loops (i.e. state variables can influence ratet of change of state variables)

E.g. Reservoir with fixed inflow and outflow

• Outflow is not necessarily a direct function of the inflow rate

• For large inflow rates the current water level may be low or high

• A correct description of the system: integration of inflow and outflow over a certain time period, initial value of the state variables has to be known for a certain point of time

Advantages

• No experiments on the original system are needed -> no threat to the real system

• Models are just size -> can represent very small and very large things

• Models produce results in shorter time periods with less money

• System behavior, dynamics and some patterns are noticeable

• Models can make test and predictions

Disadvantages

• Models are not the original -> uncertainties present

• Models include some approximations

• Models do not behave exactly like the things they represent

• Models sometimes oversimplify the process leading to misunderstandings

Conservation of mass

• for any system closed to all transfers of matter and energy, mass can neither by created or destroyed

Continuity Equation

• The rate at which mass enters a system is equal to the rate at which mass leaves the system

Reactors are systems in which chemical, biological and physical processes (reactions) proceed in a controlled manner

In ideal reactors, transport and mixing processes can be exactly mathematically described

Ideal reactors are a theoretical concepts which is analyzed instead of the real-world system to be simulated

Reactors can be technical systems (constructed) or be applied to natural systems

Batch reactor

• no inflow

• no outflow

• homogenous mixing

• constant volume

Continuous Stirred-Tank Reactor (CSTR)

• Inflow and Outflow are equal

• Stationary state

• Volume constant

• Well mixed

In addition to suitable numerical methods (models), adequate and reliable data on water quality and substance flows are the most important input parameters for system analysis

The self-regulation Ordinance (EKVO) and the Wastewater Discharge Act (AbwAG) regulate the type and extent chemical/ biological tests to ensure proper plant operation

Testing conditions are optimal -> plant and operatinf conditions change slowly

Tests are conducted on site -> manual or continuous on-line monitoring

Data monitoring results are kept in data archive

-> Generally, an extensive database in regard to water volumes and concentrations

Wastewater samples (usualy once per month)

• influent after screens or grit chamber

• Outflow of primary settling tank (without any return sludge)

• Effluent of secondary settling tank or at plant effluent

Parameter

• Homogenized samle (aliquot) - COD, TOC, Ntot and Ptot

• Filtered sample NH4-N, NO3-N and NO2-N

• Original wastewater sample - pH-value, temperature and dissolved oxygen

Continous flow measurement

Magnetic flow meter

• Measurement in a insulated, non-ferromagnetic tube

• Generation of a magnetic field

• Voltage generated (Ui) is proportional to the flow veloctiy

Self-regulation Ordinance (EKVO) requires solely visual inspection of inlet and outlet system components and regular monitoring of equipment operation (every 2 months or trimestral)

Regular and fixed monitoring testing fo not take place

Testing conditions are not adequate -> seasonal changes in flow and conenctrations

Testing campaigns are a result of specific thechnical problems

Data acquisition and data archive is non-existing

-> database in regard to water volumes and concentrations is not consistent