Trattamento delle acque reflue

2 Summary ............................................................................................................................... 3

Introduction ........................................................................................................................... 9

Importance of water availability in human activities ........................................................ 9

An example from glass manufacturing process ................................................................ 9

Fundamentals about water quality and properties ........................................................... 11

Fundamentals about water and wastewater treatments ................................................... 12

WWWT Process engineering fundamentals: BFD, PFD, P&I diagrams ............................ 13

BFD diagrams ................................................................................................................. 13

PFD diagrams .................................................................................................................. 13

P&I diagrams .................................................................................................................. 14

Process Simulation and Process Simulator ......................................................................... 17

Mathematical model of a process .................................................................................... 17

Process simulation for process design and process rating .............................................. 18

Examples ..................................................................................................................... 18

Recalling units of measurement in WWWT processes ............................................... 19

How to build a mathematical model of a WWWT process ............................................. 20

Example: writing a mathematical model of a WWWT reactor ................................... 21

A real example: reducing sulphates by Calcium hydroxide ........................................ 23

Types of operation of industrial WWWT processes ........................................................... 25

Mass balance in a batch reactor with 1st order kinetics ............................................... 27

Definition of conversion, i.e., pollutant removal ............................................................ 28

Bulk concentration and site concentration ...................................................................... 29

A real example: reducing sulphates by Calcium hydroxide ........................................ 30

General models for ideal reactors ....................................................................................... 32

Different ideal reactor models: the CSTR ....................................................................... 323

Different ideal reactor models: the PFR ......................................................................... 33

Comparison between ideal reactors: CSTR versus PFR ................................................. 36

General model of an industrial chemical & biological real reactor .................................... 40

The geometry of a real reactor ........................................................................................ 40

Model for a real reactor ................................................................................................... 40

Comparison between CSTR and PFR in terms of conversion ........................................ 44

CSTRs and PFRs connected in series and in parallel ..................................................... 45

PFR with partial recycle .................................................................................................. 47

CSTRs in series: a third way of representing mixing ..................................................... 50

Is it important to add a reactor with an external recycle? ........................................... 50

Aeration systems and mixing .......................................................................................... 51

Fundamentals of reaction thermodynamics and kinetics .................................................... 52

Methods to measure the reaction rate ............................................................................. 53

Bulk concentration and site concentration calculation ................................................... 54

Correlation of parameter values of reaction kinetic models ........................................... 57

Enzyme catalysed reactions: Michaelis-Menten reaction rate model ............................. 61

Example of models for enzymatic reaction rates ............................................................ 62

Immobilized enzymes and effectiveness factor .............................................................. 64

Microorganisms in water and wastewater treatment systems ............................................. 66

Remarks on the Monod kinetics ..................................................................................... 71

Model of an axial-dispersion biological reactor ................................................................. 72

Solving of a biological CSTR model analytically .......................................................... 73

Operation of a biological CSTR for WWWT ................................................................. 74

The wash-out ....................................................................................................................... 75

Bioreactors with thickening and partial biomass recycle ................................................... 77

The Solid Retention Time (SRT) is an operating variable ............................................. 824

Calculation of S from the Solid Retention Time (SRT) ................................................ 83

Calculation of X from S ............................................................................................... 84

Calculation of X from X .............................................................................................. 84

Summary ......................................................................................................................... 84

Biological CSTR with and without recycle: a comparison ................................................. 85

Wash-out in activated sludge system with settler and recycle ............................................ 85

Definition of SRT with incomplete mixing ........................................................................ 86

Steady-state: a useful graphical representation ................................................................... 87

Reactors for cell cultures (inoculum preparation) ............................................................... 91

Fed-batch Reactors for cell cultures (inoculum preparation) .......................................... 92

Definition and measurement of organic carbon in water .................................................... 95

Definition and measurement of solids in water ................................................................... 99

Definition of SRT with X > (and perfectly mixed reactor) .......................................... 100S

Effect of X > on the BOD of the treated water ........................................................ 100S

Reaction rate measurement if microorganisms are present ............................................... 103

Models for sizing and rating a gravity settler .................................................................... 105

Exercise ......................................................................................................................... 106

Solution ......................................................................................................................... 106

Oxygen requirement for carbon biological degradation ................................................... 109

Process Loading Factor (F ) and Sludge Volume Index (SVI) ........................................ 111C

Fundamentals about N and P removal .............................................................................. 113

Stoichiometry of biological nitrogen removal .................................................................. 113

Nitrification ................................................................................................................... 113

Denitrification ............................................................................................................... 115

Process flowsheet for biological nitrogen removal ........................................................... 115

Biological nitrogen removal: key design parameters ........................................................ 1165

Oxygen requirement for carbon and nitrogen degradation ............................................... 118

Phosphorus removal from WWWT .................................................................................. 119

Performance calculation of a nitro-denitro biological system ...................................... 119

Solubility of oxygen in water ............................................................................................ 123

Mass transfer of oxygen from gas phase to water ............................................................. 123

Mass transfer of oxygen from gas phase to water ............................................................. 125

Models for sizing and rating a gravity settler ................................................................... 126

The main pieces of equipment in a gravity thickener ....................................................... 132

Alternatives to gravity settling for sludge thickening ....................................................... 132

Flotation as another solid separation process .................................................................... 135

Design of air flotation units .......................................................................................... 136

A comparison between flotation and gravity thickening .................................................. 137

Filtration and centrifugation ............................................................................................. 139

General flow-sheet of a WWWT process and plant ......................................................... 141

Another option: Sequencing Batch Reactor (SBR) operation ...................................... 142

Adsorption Fundamentals ................................................................................................. 145

Adsorption and adsorption processes ............................................................................ 146

Adsorption Equilibria calculation ................................................................................. 147

Adsorption Equilibrium Processes: batch operation ..................................................... 150

Adsorption Equilibrium Processes: continuous operation ................................................ 151

Adsorbent regeneration and recycling .............................................................................. 154

Fixed-bed Adsorption ....................................................................................................... 154

Fixed-bed Adsorption model ........................................................................................ 156

Fixed-bed Adsorption models ....................................................................................... 160

Sludges from a WWWT plant ........................................................................................... 161

Some properties of domestic wastewater sludges ......................................................... 1616

Sludge Treatment Processes .......................................................................................... 162

Composting (aerobial) ....................................................................................................... 164

Sludge Aerobic Digestion ............................................................................................. 165

Sludge Anaerobic Digestion ............................................................................................. 168

Anaerobic Digestion Process Schemes ......................................................................... 169

Anaerobic and Aerobic Digestion Processes: a comparison ............................................. 171

Process Control Fundamentals .......................................................................................... 173

Control (regulation) Loops in WWWT plants .............................................................. 174

Extra: Microalgae in wastewater treatment ....................................................................... 175

Microalgae metabolism ................................................................................................. 175

Microalgae nutrient incorporation ................................................................................. 176

Microalgae composition ................................................................................................ 176

Microalgae biomass exploitation .................................................................................. 177

Cultivation systems ....................................................................................................... 177

Microalgae in wwt: fundamental idea ........................................................................... 178

Microalgae possible use in wwt .................................................................................... 178

Microalgae in secondary treatment ............................................................................... 179

Microalgae growth kinetic ............................................................................................ 179

Microalgae in tertiary treatment .................................................................................... 180

Microalgae-bacteria consortia in wwt ........................................................................... 181

High-rate algal ponds (HRAP) ...................................................................................... 181

Examples of microalgae application in wwt in the laboratory ...................................... 182

Mixotrophic regime ....................................................................................................... 183

Effect of hydraulic retention time (HRT) ...................................................................... 184

Processes for enhanced biological phosphorus removal ............................................... 184

EBPR: general process scheme ..................................................................................... 18578

Importance of water availability in human activities

• 1. Water for living of human beings
• 2. Water for economical activities:
  • a. Water treatment plants
  • b. Manufacturing, i.e. production plants
  • c. Wastewater treatment plants
  • d. Commercial activities and community services
• 3. Sources and destinations of water resources
• 4. The price of water
• 5. Water use in the context of circular economy

An example from glass manufacturing process

In the glass manufacturing industry, the main uses of water are related to cleaning, cooling systems and hot glass rejects cooling systems.

Cleaning waters do not present particular issues with respect to any industrial facility, namely inert solids and typically oil.

Process waters contain fine particles of glass from fragmentation and from the action of mechanical scraper systems but also small quantities of oil from the machines and oil-water mixtures used in the shear and delivery mechanisms.

Wherever practicable, such type of water can be readily recycled or treated using standard techniques in a closed-circuit cooling system. 9

Open circuit cooling is generally used to handle more rare, severe incidents when large quantities of hot glass must be cooled (a major furnace leakage or other accidents causing the interruption of forming operations).

This water is to be considered as a utility fluid.

• First of all, the process has to be represented by a flowsheet.
• Second, the water duties have all to be identified.
• Third, the net water consumption has to be calculated.
• Fourth, the water qualities have to be evaluated in all make-ups and in all purges.

At this point Only, a water and a wastewater system can be designed.

This is an example of the usual water treatment process for a glass factory.

There will be another one for the wastewater treatment process10

Fundamentals about water quality and properties

• 1. Bulk properties of water as a pure component: density, vapor pressure, specific heat capacity, surface tension... Values and temperature effect
• 2. Real water is always a multicomponent system:
  • a. Water is however the dominant component (>99.99% by mass)
  • b. Other components: dissolved species, suspended solids
  • c. Dissolved species: other liquids as well as gases and solids
  • d. Remind the difference between single-phase and two-phase systems
• 3. The presence of other components in water is usually evaluated in terms of composition (mg/l, ppm, ppb, molar, mass). Why 1 mg/l 1 ppm?
• 4. Also waste water is always a multicomponent system. However, the presence of the might be up to some % points
• 5. Bulk properties of water are Not affected by the presence of pollutants
• 6. Interactions with the human body (i.e., their biological activity)

The required water or wastewater quality is a function of its intended use: potable (drinkable) water, toilet water, bathing water, rain water, water for agriculture, water for aquaculture, industrial water (as process water), industrial water (as utility, i.e., mean to transfer heat)

The required water or wastewater quality is established by either technical constraints or regulatory constraints

The «value» of a water is affected by the presence and concentration of the other components

To sum up:

• The cost of water production depends on its intended use
• The cost of water and wastewater treatment depends on the type and concentration of pollutants 11

Fundamentals about water and wastewater treatments

Unwanted components in water may be of organic type, inorganic type, as well as micro-organisms, i.e., living components (bacteria, viruses).

These unwanted components can be removed from water by using a number of industrial processes based on different techniques1.

These techniques are usually divided in four categories, accor