Embed Size (px)
Citation preview
Dr Bill Barber 12th June 2012
The Wastewater Treatment Plant of tomorrow
Our Current wastewater treatment design
Evolved from 19th Century Drivers
- Public health • Removal of disease causing organisms (Cholera, typhoid)
- Pollution (of rivers) • Contaminant removal
Consequently most plant is based on mainly 19th Century tech
- Primary settlement
- Activated sludge
- Anaerobic digestion
The Wastewater treatment plant of today
Screening Primary Settlement
Activated Sludge
Nutrient Recovery
Thickening Pre -treatment
Anaerobic Digestion
Energy Recovery
Dewatering Biosolids to land
Final effluent
1872 1858 1914 1857
1955 1976 1895 1860 1857
1820s 1900
1846 1854 1857 1858 1859 1863 1867 Liming Activated
carbon Filter press dewatering
Primary settlement, electricity
Thermal drying
Freezing Struvite Precipitation
1871 Ammonium recovery by
steam stripping
1872 Screening and straining to allow use of sludge
water for irrigation
1872 Advanced thermal drying with heat
recovery
1880s Interest in fermentative
putrefaction (anaerobic digestion)
1887
Anaerobic sand filter
1890
Agricultural products
from sludge
1895
Exeter (septic)
tank
1902
Staged anaerobic digestion
1906
Theory of AD for biogas
prediction
1910
Imhoff tank
1916
Wet air oxidation of
sludge
1935
Microwave pretreatment
for AD
1965
Thermal hydrolysis of
ligno-cellulosic material
1969
Anaerobic filter
1970s
Acid phase AD also with pre-
treatment (ultrasound)
Late 1970s Upflow Anaerobic Sludge Blanket
1980 Anaerobic fluidized
bed
1990s Anaerobic membrane
bioreactor
1914 Activated
sludge
Use of technology designed to meet 19th Century Drivers
- We rely on activated sludge and variants • High energy consumption • Produces secondary sludge which doesn’t
digest well (Rudolfs and Heisig, 1929)
- We still design anaerobic digestion plants which are inherently sub-optimal • Current best practice is to build new plants which
already need pre-treatment bolt-on to improve performance
• Design has not evolved in over 120 years
- They are not designed for modern drivers • Energy and carbon inefficient • Not designed for recovery of value
A carbon footprint? What is one of those?
Why has the design of anaerobic digestion not progressed?
- Energy production was not the primary driver (and in NA, relatively cheap)
- Conservative industry led by meeting regulatory requirements. Energy production is/was not core business
- Text book rule of thumb based on previous conservative designs
WEF, cited in M&E 4th Edn.
- Not due to lack of understanding of microbiology
4C8H13N2O3 + 14H2O = 4N2 + 19CH4 + 13CO2 + 2H2
Rideal, 1906
Water Industry Advanced Anaerobic Digestion
Chemical Lysis Medium Pressure Maceration Rapid Decompression
Thermal Hydrolysis Biological Hydrolysis Acid Phase
Electric Pulse Ultrasonics High Pressure Shear
Current performance – Anaerobic Digestion
This is best practice
Anaerobic Digestion Anaerobic Digestion
100% 42%
58%
Issues with current design of anaerobic digestion - We (almost always) digest in parallel
• But microbiology of anaerobic digestion is a series of reactions
59% VSR
66% VSR
59%
59% 18%
71% VSR 59% 18% 13%
In Practice – Tacoma Central, USA
57% VSR
67% VSR
57%
57% 23%
In Practice – Budd Inlet, USA
Issues with current design of anaerobic digestion - We co-digest primary and waste activated sludge but they
are fundamentally different materials with: Very different C:N ratios Different calorific values Different kinetics governing their degradation Different biogas yield per kg destroyed Different biogas composition Different temperature optima Work has shown when primary and secondary sludge are
digested separately, biogas production is higher than when an equivalent mixture of the sludge is digested together
Separate Primary and WAS digestion
Separate Primary and WAS digestion
Issues with current design of anaerobic digestion - We don’t keep the biomass in the digesters
• The biogas producing organisms are known to be slow growing • We do this for activated sludge treatment • Recuperative thickening attempts to address this • Loading rates are low and therefore digestion plants are
unnecessarily large
Speece, 1983
Primary Sludge
C23H35O8N
Fibre
Protein
Carbohydrate
Fat
C7H11O3N
Waste Activated Sludge
Fibre
Protein
Carbohydrate
Fat
Digestion and burning of primary sludge Basis: 10,000
TDSA
Input
In Biogas
Electricity output
Heat
In biosolids
6.16 MW0.00 MW
3.91 MW0.00 MW
1.45 MW
For digestion0.51 MW
Surplus1.52 MW
2.26 MW0.00 MW
2.03 MW
Lost0.43 MW
Electricity output0.25 MW
Efficiency losses1.57 MW
Required for pre-drying0.44 MW
6.16 MW0.00 MW
3.91 MW0.00 MW
1.45 MW
0.51 MW
1.52 MW
2.26 MW0.00 MW
2.03 MW
0.43 MW
0.25 MW
1.57 MW
0.44 MW
Digestion and burning of WAS
Input
In Biogas
Electricity output
Heat
In biosolids
5.20 MW0.00 MW
1.71 MW0.00 MW
0.63 MW
For digestion0.51 MW
Surplus0.38 MW
3.49 MW0.00 MW
0.89 MW
Lost0.19 MW
Electricity output0.20 MW
Efficiency losses1.27 MW
Required for pre-drying2.02 MW
5.20 MW0.00 MW
1.71 MW0.00 MW
0.63 MW
0.51 MW
0.38 MW
3.49 MW0.00 MW
0.89 MW
0.19 MW
0.20 MW
1.27 MW
2.02 MW
Basis: 10,000 TDSA
Current performance – Dewatering
This is best practice
Dewatering
Where the industry wants to go
- Maximize the value of biosolids application to land as a low-carbon intensive sustainable fertilizer • Costing analyses done in 1860s, most turned a profit • Patents on sludge use as fertilizer 1890s
- Recover resources • But we still rely on secondary treatment which involves the
destruction of resources (even deammonification) The world consumes energy to make nitrogen resources for
agriculture then wastewater treatment consumes more energy to destroy them
• Struvite Patented 1857 for extraction of “ammoniaco-magnesian phosphate”
• Ammonia, as ammonium sulphate From steam stripping, patented in 1871
- Enhance energy recovery • As previously mentioned
21st Century Drivers
21st century Drivers - As with the Victorian Sanitation engineers, the wastewater
treatment plant of the future will be fundamentally influenced by a number of non-regulatory and regulatory drivers
- It is likely that the technology of the future plants will be based on variations of what currently exists and technology currently at lab- or pilot-scale
Population Growth
1804
1927
1960
1974
1987
1999
2012
+123
+33
+14
+13
+12
+13
Higher population which is more affluent
Increasing affluence – changing eating habits
Changing eating habits
Production of beef requires > 70 times the energy and 25 times the water than an equivalent weight of
corn
Changing food habits
0
2,000,000
4,000,000
6,000,000
8,000,000
10,000,000
12,000,000
1700 1750 1800 1850 1900 1950 2000 2050
Phos
phor
us R
equi
rem
ent [
t/yr]
Year 0.6 kg P/pop.yr 1.6 kg P/pop.yr
Urbanization
0
10
20
30
40
50
60
70
80
90
100
World Africa Asia Europe Latin America
North America
Perc
enta
ge
1950 2007 2030 (predicted)
Impacts of climate change
• Sewer flooding • Environmental impact of
intermittent discharges • Environmental and
regulatory threat from pollution incidents
• Security of supply • Water quality • Increasing flood risk • Indirect, socio-economic
risks
Recovery of phosphorus? Phosphorus Balance
Adapted from Cordell et al., 2009. The story of phosphorus: Global food security and food for thought
Mined P Rock
P Fertilizer
Production Arable Soil Crops Harvested
Crops Food
Commodities Humans
Animal Manure
Domestic Animals
Organic Waste Excreta Other
Uses
Phosphate Rock
Reserves
Non-food
Inland Coastal Waters
17.5
Mining losses
Distribution losses
Erosion losses
Crop losses Harvest losses Food-chain losses
Natural Environment
Anthroposphere
14.9 14 12 7 2 2.6
3.5
0.6
3
1.8
0.9 0.8 8 3 0.9 1
1.2 3 1.2
1.5
0.2 0.3
Annual figures in millions of tones
0.9
7 12.1
15
8
Anyway, a third of all food is thrown away
Phosphate Reserves (65,000 million tonnes)
Source: Van Kauwenburgh (2010) World Phosphate reserves and resources, IFDC
Jordan
Brazil
Russia
Rest
Morocco & WS
85%
China
6% United States
3% 2% 1% 1% 2%
Where could we go from here - Improve anaerobic digestion
• As we have seen, many options exist, starting with series digestion and solids retention
• Hydrolysis technology will always improve any anaerobic digestion configuration
• AnFB + AnMBR gives effluent equivalent to activated sludge treatment at under 50F for influent wastewater
- Improve dewatering • It is not the dewatering equipment or the polymers
which are limiting performance but, it is the sludge itself
• As for anaerobic digestion, employ pre-dewatering technology to change biosolids properties
- Is biogas the answer? • It is the natural endpoint of fermentation
Minimize energy consumption at a wastewater treatment works - We know that diverting carbon away from secondary
treatment towards anaerobic digestion is highly beneficial regarding site-wide energy balance • Less load to secondary requires less aeration energy • More sludge is produced so there is more biogas • Higher proportion of primary sludge Which has higher calorific value Generates a higher biogas yield Is more biodegradable
- What is the logical endpoint of this approach?
The Wastewater treatment plant of today
Screening Primary Settlement
Activated Sludge
Nutrient Recovery
Thickening Pre -treatment
Anaerobic Digestion
Energy Recovery
Dewatering Biosolids to land
Final effluent
The Wastewater treatment plant of today
Screening Primary Settlement
Activated Sludge
Nutrient Recovery
Thickening Pre -treatment
Anaerobic Digestion
Energy Recovery
Dewatering Biosolids to land
Final effluent
The Wastewater treatment plant of tomorrow?
Screening Primary Settlement
High Rate Anaerobic Digestion
Thickening Anaerobic Digestion
Pre- dewatering
Energy Recovery
Dewatering Biosolids to land
Nutrient enriched irrigation water
Energy Recovery
On-site processing
Off site organics
Start with anaerobic digestion first?
Extracting value from biosolids
Metals
"There are metals everywhere," Dr. Kathleen Smith of the US Geological Survey (USGS) said in a statement, noting that they are "in your hair care products, detergents, even nanoparticles that are put in socks to prevent
bad odors."
Biosolids as a resource
From purely a financial standpoint, are we recovering the right materials?
185 kg
$100+
Operation of tomorrows wastewater treatment plant
- Data and online monitoring
- High level of automation
- Remote (unmanned) operation
- Advanced telemetry • Intelligent unit operations
- Smart metering
- Self correction in real-time
- Communication between sites
Conclusions Our wastewater treatment plants of today are based on drivers from the 19th century and are therefore inefficient at meeting the desires of modern operators
As for 19th the century, a variety of modern drivers, which may be regulatory or non-regulatory, will shape the development of 21st century wastewater treatment plants
The treatment plant of tomorrow may comprise a combination of optimised variants of what we have today and new technology and will use highly advanced data management and control systems, assuming drivers encourage change
Modern facilities will have to adapt to climate change, increasing demands on water, energy and resources
