Seperation Technologies Flashcards
Solid-Liquid Treatment
Why solid-liquid seperation?
- To obtain a liquid with less or no
solids or having solids with less
or no liquid - Both/a combination of the two
A typical situation in environmental technology is wastewater containing solids or dissolved pollutants that will be trapped as solids and then separated before the treated wastewater is released to a recipient.
What are technologies which may be used for seperation?
E.g. mechanical, adsorption, chemical, biological, thermal or electrical.
The different mechanisms utilise different driving forces and thus need different efforts for
accomplishing the separation processes.
Different techniques can be combined for greater efficiency.
Aspects to consider when choosing technique for solid-liquid treatment:
- Physical and chemical characteristics of both solids and liquids
- If it is a mix of different particles (or matter) we want to separate from the liquid.
- To obtain a liquid with less or no
solids or having solids with less
or no liquid - Desired characteristics of products
- Nature of the process
- Resources available
o Economic value (feasible or reasonable in relation to the price/value of separation
process)
o Time (process time)
o Space (physical space available)
o Personnel and operation needs
o Knowledge (advanced operation)
What could the particles be?
- Solids
- Colloidal particles (Ø < 1 micrometre)
- Dissolved solids (Ø < a few nanometres)
- Dissolved molecules and ions. These are not “solids”
per se but could be treated in order to form removable
solids or by chemical entrapment.
What are important water quality parameters to consider in solid-liquid seperation processes?
BOD Biological Oxygen Demand: a measure of organic
matter. Amount of oxygen dissolved in the liquid
consumed by micro-organisms for the degradation of the
organic matter.
COD Chemical Oxygen Demand: the amount of oxygen
needed to completely oxidise (decompose) the organic
content in the water. BOD is a measure of what can be
decomposed by the biological system (micro-organisms)
while COD is the measure of all material that can be
oxidised.
SS Suspended Solids: organic and inorganic substances
present in the water.
Hazardous/toxic substances that could be either
molecules or ions.
What is screening used for in solid-liquid separation?
Screening is a basic technique to remove large particles and debris from liquid based on particle size, usually as a pre-treatment.
Advantages:
Simple and cost-effective.
Disadvantages:
Only effective for large particles and not for fine solids.
How does sedimentation work?
Particles settle by gravity in a liquid. It is divided into free settling (particles don’t interact) and hindered settling (particles form sludge).
Advantages:
Low energy requirements.
Disadvantages:
Slow process, may require chemical aids (e.g., flocculants) to improve performance.
What are clarifiers and thickeners used for?
Clarifiers: Remove particles to obtain a clear liquid.
Thickeners: Concentrate solids in sludge.
Advantages:
Effective for large-scale industrial processes.
Disadvantages:
Requires regular maintenance to handle sludge build-up.
What is the purpose of coagulation and flocculation?
To combine small particles into larger flocs that can settle more easily. It involves adding coagulants like metal salts (e.g., aluminum or iron salts).
Advantages:
Speeds up sedimentation and improves the clarity of liquid.
Disadvantages:
Requires chemical additives which may increase costs and require disposal
How does chemical precipitation work in solid-liquid separation?
It involves changing the chemical conditions to make dissolved substances form solid particles that can then settle or be removed.
Advantages:
Removes dissolved substances that other methods can’t.
Disadvantages:
Requires chemical handling and disposal.
What are the two types of biological cleaning processes?
Aerobic processes: Use oxygen to break down organic matter.
Anaerobic processes: Break down organic matter without oxygen, producing methane.
Advantages:
Can treat high-strength organic waste.
Disadvantages:
Requires careful management of conditions (e.g., oxygen levels, temperature).
How does flotation work in solid-liquid separation?
Fine air bubbles are attached to solid particles, making them float to the surface where they are skimmed off.
Advantages:
Effective for light particles.
Disadvantages:
Requires complex equipment and energy for aeration.
What is filtration in solid-liquid separation?
A process where a porous material captures particles larger than the filter pores, allowing only the liquid to pass through.
Advantages:
Simple and widely used in various applications.
Disadvantages:
Clogging is common and requires filter replacement or cleaning.
What are the four types of membrane filtration?
Microfiltration: Removes bacteria and larger particles.
Ultrafiltration: Removes viruses and colloidal particles.
Nanofiltration: Removes molecules like sugars and dyes.
Reverse osmosis: Removes ions and salts.
Advantages:
Highly effective for removing small contaminants.
Disadvantages:
Expensive membranes and requires high-pressure operation.
How does centrifugation separate solids from liquids?
Uses centrifugal force to separate heavier solids from lighter liquids by spinning the mixture at high speeds.
Advantages:
Fast separation of solids and liquids.
Disadvantages:
Requires high energy and is expensive for large volumes.
