Odour Result of biological activity on proteins and other substances in the wastewater in the absence of oxygen Odorants generated comprise volatile organic compounds and gaseous inorganic compounds such as hydrogen sulphide (H 2 S) and ammonia (NH 3 ) Major sources of odour at typical wastewater treatment facilities include: –Pumped Sewers –Inlet Works including screens –Primary Settlement Tanks/Clarifiers –Sludge and return liquor treatment areas
Odour- Analysis and Predictions Dispersion models required to convert measured or calculated odour emission rates to atmospheric odour concentrations 2 popular models available – AERMOD and ISC AERMOD is recommended by the US EPA AERMOD requires terrain and meteorological data for accurate predictions. Graphical Model Interface
Odour- Analysis and Predictions Model outputs are in the form of diagrams showing likely (98 percentile) atmospheric odour concentrations. Wind roses show prevalent wind direction for the area under assessment.
Odour- Control, Treatment and Abatement Dedicated Odour Control and Abatement Equipment include: –Dry absorbers such as carbon filters –Bio-filters and Bio-scrubbers that utilise biomass on a structured media bed. –Chemical Scrubbers that utilise acids/alkalis and oxidants. –Incinerators or thermal oxidisers that oxidise odorants in foul air. Masking Sprays may also be used to mask
What is Anaerobic Digestion? Conversion of organic matter to methane and carbon dioxide in the absence of oxygen. C 5 H 7 0 2 N+6H 2 05CH 4 + 2NH 3 + 5CO 2 + Biogas Produces stabilised residual solids. Biogas comprises approximately 60 to 65%CH 4, 30 to 35%CO 2 and other gasses.
Typical AD system Effective gas mixing Effective external heat exchangers 15 day retention Continuous feeding
Enhanced AD System Effective jet mixing Effective external heat exchangers 12 day retention Continuous feeding Pre-treatment
What does Pre-treatment do? Increase pathogen destruction –Compliance with microbial standards eg US EPA Class A –Safe use of sludge in agriculture –Applicable to wider range of crops –Secure agricultural disposal route Increase solids destruction –Increased Bio-Gas production –Increased power generation through CHP –Reduced amount of sludge requiring disposal
Reaction Steps in AD with Pre-Treatment hydrolysis acidification acetogenesis methanogenesis AD pre-treatment hydrolysis acidification pH = 5.0 to 5.5 pH ~ 7.0 to 7.5
Methods of Pre-treatment Biological Thermal Chemical Mechanical (high shear, grinding) Ultrasonic
Typical Biological System Ht Ex 1 Ht Ex 2 Ht Ex 3 cold water hot water pre-treated sludge to AD reactor raw sludge 42 o C 55 o C total retention = 2 days
Case Study-Kings Lynn STC, United Kingdom Sludge Throughput = 14,500 to 19,000tDS/year Proportion of primary to WAS = 50:50 to 35:65 Pre-treatment = Biological Volatile Solids Destruction = 50 to 60 %
Case Study-Kings Lynn STC, United Kingdom Enough power generated to support the Wastewater Treatment Plant and export to the grid
Why Adopt AD in the GCC? Slow uptake of anaerobic technologies in the region. WHY? Cheap Energy - More expensive to recover energy from anaerobic digestion than have energy supplied from the grid/other sources. BUT Landfill - There will eventually be constraints on space for landfills which is currently the preferred disposal route for sludge solids OTHER POSSIBLE DRIVERS Fertiliser - An aerobically digested sludge solids could be used as fertiliser if appropriate legislation and regulations are in place. Sustainable - Sustainable source of energy.
Nutrient removal - Introduction Essential nutrients for plant growth: –Nitrogen – Ammonia, Nitrate –Phosphorous in the form of Orthophosphate Nutrients are usually limited in natural waters and hence restrict plant and algae growth Free fertiliser where TSE is re-used to irrigate plants
Why use nutrient removal in GCC? Chlorine disinfection – Ammonia removal required Coastal discharges Prevention of eutrophication where: –TSE is re-used for lakes and water features –Storage in lagoons is primary disposal outlet for TSE.
Nutrient Removal – Ammonia Most plants in region are designed to meet re-use standards Normally will also achieve ammonia removal as well Typically ammonia is converted to nitrate via nitrification Requirements for Nitrification: –Typical Feed to Mass (F/M) Ratio = 0.15. This value increases with temperature
Background Leightons Middle East were bidding major Watewater Project in the Region Mott MacDonald were commissioned to provide a detailed tender design covering all aspects of the project including: –Civil / Structural –Geo-technical –Process –Mechanical –Electrical and ICA
Detailed Tender Design Close collaboration between all parties in the tendering team Clearly defined extent of design responsibilities between all parties involved Use of design examples / experience gained during execution of similar project elsewhere within Mott MacDonald A detailed tender design was produced making use of the skills of all parts of the team Good understanding of risks associated with the project and providing greater cost certainty to contractor and ultimate client Detailed tender stage work would facilitate rapid start following award. Key Design aspects include: –Carrying out engineering calculations for all structures and systems –Preparation of 3D Modelling of key structures