ANAEROBIC DIGESTION OF MUNICIPAL WASTE PRESENTED BY: Mr. Thomas McAndrew Ms. Ciara Coughlan Ms. Ann Phair

Anaerobic Digestion of Municipal Sludge Introduction Types of waste treated by A.D. A.D. of municipal Sludge

Municipal Sludge Composition of sludge W.W.T.P. produce two types of sludge: primary sludge Secondary sludge

Municipal Sludge Feedstock for A.D. Toxic substances Bioagents Disinfectants Long straw Quality and Quantity - why important Quality For good quality biogas need high organic matter Quantity How much will depend on which products are a priority Can leave dormant

Pre-treatment of Municipal waste Why? Aerobic v’s anaerobic Screening and grit removal Primary sedimentation Secondary treatment Sludge thickening using a picket fence thickener

Case Study of Tullamore Treatment Plant Secondary treatment Biofilm tanks

Case Study of Tullamore Treatment Plant Sludge thickener used Picket fence thickener

Case study of Tullamore Treatment Plant Post anaerobic digestion Belt Press machine

Definition of Anaerobic digestion Anaerobic digesters produce conditions that encourage the natural breakdown of organic matter by bacteria in the absence of air.

The Microbiology Of The Process This occurs in 4 stages: 1) Hydrolysis 2) Acidogenesis 3) Acetogenesis 4) Methanogenesis

Metabolic Stages of Production of Methane 1 st Stage Hydrolysis C 6 H 10 O 4 + 2H 2 O C 6 H 12 O 6 + 2H 2 2 nd Stage Acidogenesis Decomposition of products

Metabolic Stages of Production of Methane 3 rd Stage Acetogenesis C 6 H 12 O 6 2CH 3 CH 2 OH + 2CO 2 4 th Stage Methanogenesis CO 2 + 4H 2 CH 4 + 2H 2 O

Biological Process

Parameters for Optimum Digestion Temperature pH Carbon to Nitrogen Ratio

Basic Components Of Anaerobic Digesters 1) Feedstock Storage 2) Handling System 3) Digestion Tank 4) Gas and Residue Recovery Systems

Type of AD Systems Anaerobic Lagoons Contact Stirred Tank Reactor (CSTR) Upflow Anaerobic Sludge Blanket Reactor (USAB) Fixed Film Anaerobic Filters

Parameters for Optimum Digestion Temperature Carbon to Nitrogen Ratio pH

Products of A.D Biogas Fibre Liquor

Biogas methane carbon dioxide hydrogen sulphide ammonia

Using the biogas Heat the digester Generate heat Cooking Convert it to electricity Combined heat and power (CHP) plant

Digestate Remains after the gas has been removed –Fibre –Liquor

Fibre Contains Plant nutrients No odour Uses Low-grade fertiliser Alternative to peat

Liquor Low level but a large range of nutrients A high water content Used as a liquid fertiliser Lagoons or large tanks Produce small amounts of methane

The Advantages of A.D Wide range of organic Reduction approximately 80% of the odour potential Boost the local rural economy Reducing land and waste pollution A.D provides on site energy for the process

The Disadvantages of A.D Create traffic movement Generate noise The liquor and the fibre can contain animal by products Rigorous monitoring of wastes