WATER QUALITY MODELING AND

PREDICTION

>> Muhammad bin Ramlan

CONTENT AN ALGAL BIOMASS PREDICTION MODEL

Introduction Nutrient Cycling The Nitrogen Cycle Phosphorus Cycle Silica Cycle Summary of Nutrient Cycles

Simulation Method Introduction Numerical Accuracy Traditional Approach Backtracking Approach Model Uncertainty

CONTENT AN ALGAL BIOMASS PREDICTION MODEL

Introduction Nutrient Cycling The Nitrogen Cycle Phosphorus Cycle Silica Cycle Summary of Nutrient Cycles

Simulation Method Introduction Numerical Accuracy Traditional Approach Backtracking Approach Model Uncertainty

INTRODUCTION

Simulation model: DELWAQ-BLOOM

This model is used to predict algae growth and mortality, oxygen concentrations and nutrient dynamics

This model process can be grouped into: nutrient cycling, algae modeling, and oxygen-related process.

NUTRIENT CYCLING

The DELWAQ-BLOOM model assumes that algae consumes ammonia and nitrate in the water column.Optionally the model includes algae species with the ability to take up atomic nitrogen and detritus.

THE NITROGEN CYCLE

The nitrogen cycle consider the water-column components• e.g. ammonia, nitrite and

nitrate, algae, suspended detritus and suspended (non-dertitus) organic nitrogen.

Two important reaction in the nitrogen nutrient cycle • Nitrification and

denitrification• nitrification

(production of nitrate in system) and denitrification (nitrate is removed from the system).

• These reaction affect the flux of ammonia and nitrate in the water column.

PHOSPHORUS CYCLE

A simplified version of the nitrogen cycle

The specified reaction of this cycle is the absorption / desorption of particulate inorganic phosphorus

SILICA CYCLE

A simplified version of the nitrogen cycle

The specified reaction of this cycle is there is no absorption of silica to inorganic suspended solids.

SUMMARY OF NUTRIENT CYCLE

The nutrient cycle just described are based on the assumption that

nutrients can be recycled an infinite number of times without any loses

other than due to transport, chemical absorption, denitrification

and burial.

CONTENT AN ALGAL BIOMASS PREDICTION MODEL

Introduction Nutrient Cycling The Nitrogen Cycle Phosphorus Cycle Silica Cycle Summary of Nutrient Cycles

SIMULATION METHOD Introduction Numerical Accuracy Traditional Approach Backtracking Approach Model Uncertainty

INTRODUCTION

Simulation Method – water quality models

Numerical

Accuracy

Traditional Approach

Backtracking

Approach

NUMERICAL ACCURACY

Water quality simulation models based on physical,

biological and chemical processes typically include time rate of change terms

as dC/dt.

TRADITIONAL APPROACH

Most water quality simulation models

simulate quality over a consecutive series of discrete time periods.

Time is divided into discrete intervals and the

flows are assumed constant within each of

those time period intervals.

Each water body is divided into segments or

volume elements, and these are considered to

be in steady state conditions within each simulation time period.

At the end of each period, mixing occurs

within each segment or volume element to obtain the concentrations in the

segment or volume element at the beginning

of the next time step.

BACKTRACKING APPROACH

Backtracking approach eliminates the need to consider the simulation time-step duration restriction. The backtracking approach permits any simulation time-step duration to be used along with any segmenting scheme.

Unlike the traditional approach, water can travel through any number of successive segments or volume elements in each simulation time step.

Instead of following the water in a segment or volume element downstream, the system tracks back upstream to find the source concentration of the contaminants.

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