Transcript Anaerobic/Aerobic - Small Island Developing States Network

Opportunities for Sectoral
Synergy in Public Sector Waste
Management
UNDP Waste Management Experts Meeting
Havana, Cuba, October 27 - 31, 2003
Authors:
Hugh Sealy, Ph.D., P.Eng.
Kev L. Metcalfe, P.Eng.
Norm J. Nuttall, P.Eng.
Stantec Consulting International Ltd.
Introduction
• In many Caribbean countries, there exists the
potential for cooperation between the agencies
responsible for solid waste and domestic wastewater
(sewage) management, which would result in
improved operations, increased environmental and
economic benefits and reduced risks.
Cooperative Approach
Economic
Benefits
Environmental
Benefits
Risk Management
Benefits
Result: Improved Operation and Reduced Costs
Constraints to Cooperation
Unfortunately, this potential synergy tends to be
unrealized, perhaps for the following reasons:
• Responsibility for solid waste management and
wastewater management usually resides within
separate departments/ministries.
• The concept of an integrated approach to both waste
management (solid, liquid and gas), including
residuals management is not yet pervasive within
the region.
• Funding tends to be project specific and linear in
programming and does not allow for inter-agency
cooperation.
Constraints to Cooperation
• Traditionally, low tech approaches have been
used for SWM in the Caribbean, whereas it
may be argued that WASA’s have been
exposed to more complex technologies in
the treatment and delivery of potable water
and the treatment and disposal of
wastewater. For example, the Barbados
Water Authority (BWA) recently specified a
mechanical treatment plant for septage and
sludge treatment rather than “low tech”
lagoons.
Technology Evolution
Dumps
Engineered Sanitary
Landfills
Simple Lagoons
Complex Mechanical
Treatment Plants
Higher Level of Environmental Protection
Objective
• The objective of the following paper is to present
examples from the Caribbean (in particular using
case studies from the Bahamas and from Barbados)
where it can be shown that cooperation between
solid waste and wastewater utilities in residuals
management may result in benefits to both utilities.
Waste Streams & Residuals
“A” List
“B” List
Residuals (Liquids, Gases & Bio-solids)
 Leachate from landfills that have a collection system
 Landfill gas generated from the decomposition of
wastes
 Septage from septic treatment systems
 Screenings from primary sewage and septage
facilities
 Sludge (primary & secondary) from sewage
treatment plants
Other Residuals
 Grease from food preparation
 Used motor oil
 Sludges from car washes
 Blood and by-products from abattoirs
 Manure
 Petroleum contaminated soils
Disposal Options for Residuals
Leachate
1. Anaerobic / Aerobic lagoons with mechanical
aeration
 Effective treatment
2. Recycle leachate by re-circulating it through the
landfill
 Increased waste decomposition of solid waste in landfill
 Reduced strength of leachate
60,000
Flow (gal./day)
50,000
Estimated
Quantity of
Leachate
Generated
40,000
30,000
20,000
Estimated Quantity of
Leachate Requiring
Treatment and Disposal
10,000
0
0
4
8
12
Year
16
20
Disposal Options for Residuals
Landfill Gas
 Collected and flared or used to produce energy
 Passive venting
 Re-circulation of leachate can affect rate of gas generation
 Approximately 40 to 80 tonne per day landfill site could
generate 1 MW of energy
Disposal Options for Residuals
Septage
 Series of lagoons: settling pond, anaerobic and
aerobic
 Incorporated into Primary Sludge disposal
Disposal Options for Residuals
Sewage Sludge
Primary Treatment Sludge:
 Direct disposal to dedicated cells on site
 Primary digestors at treatment plant
Secondary Treatment Sludge:
 Co-composting
 Landfarming
 Lagoons
Disposal Options for Residuals
Screenings:
 Dedicated cells
 Landfilled
 Co-composting
Synergistic Residuals Management
Options
The following two technologies may
provide opportunities for co-disposal
of residuals in the Caribbean:
• Bioreactor Landfill
• Co-composting
Bioreactor Landfill
 Designed to rapidly change and biodegrade
organic component of solid waste stream
 Adding sufficient liquids and air
 Aerobic, Hybrid and Anaerobic
Waste Age, Phil O’Leary & Patrick Walsh, June 2002, p.64
Bioreactor Landfill
Most Easily Adapted to Caribbean: Anaerobic.
 Moisture content most important aspect. Upwards of 65% required.
Recirculating leachate alone (at least in the initial stages of the
landfill life) may not achieve the desired moisture content.
 Leachate, storm-water, screenings, sewage sludge, septage and
other waste treatment effluents can be added to achieve the desired
moisture content.
 Benefits: Accelerated decomposition, reduced leachate treatment
and disposal costs, reduced need for leachate treatment facilities,
reduced post closure costs and increased landfill gas generation.
Leachate Generation
Estimated Leachate Generation Quantities – New Providence
Year of Landfill
Operation
Annual Leachate Quantity
(cu. ft.)
4
80,000
8
500,000
12
1,000,000
16
2,500,000
20
2,000,000
Co-composting
 Defined as: composting of organic waste
supplemented with a range of materials (e.g.
septage, sludge, abattoir wastes).
 Carbon to Nitrogen Ratio (C:N) is key. The ideal
C:N ratio is 25-30:1. The C:N ratio of MSW has
increased over the years as the paper content has
increased. A typical MSW ratio is now 60:1. To
lower the C:N ratio, the modern trend is to add
sewage sludges. The following table describes the
C:N ratio of various materials.
C/N Ratio of Various Wastes
Material
C/N ratio
Night soil
6-10
Urine
0.8
Blood
3.0
Cow manure
18
Poultry manure
15
Horse manure
25
Raw Sewage sludge
11
Activated sludge
6
Grass clippings
12-15
Sawdust
200-500
MSW
60
Co-composting Cont.
 Simple windrow facility to enclosed reactor
 Successful co-composting mixtures:
•
•
•
•
•
•
MSW organics / secondary sewage sludge
Septage solids / wood chips
Abattoir wastes / yard wastes
Chicken manure / yard wastes
MSW organics / septic tank pump out waste
MSW organics / fishery wastes
Typical Small Island State Operations
 Leachate: left in the landfill, treated,
recycled or released
 Landfill Gas: ignored, passively vented
 Septage: lagoon treatment, effluent
discharged
 Screenings: landfilled, dedicated disposal
cells
 Sewage Sludge: stored, land spread
 Other Residuals: uncontrolled
Caribbean Case Study- Bahamas
New Providence
New Providence Sanitary Landfill
 Operated by DEHS
 60 mil HDPE Liner
 Leachate Collection
 Gas Collection Piping Installed
Septage & Sludge Facility
 Operated by W&SC
 HDPE Liner
 Treats waste from septic tank
pumpouts
Present Situation in New Providence
Landfill Leachate
Septage &
Sludge
Treatment
(Lagoons Future)
Liquid
Disposal
(Deep Well)
Lagoons
(Anaerobic/Aerob
ic)
Liquid
Disposal
(Deep Well)
Drying
Beds
(Future)
Cooperative Approach
Septage & Sludge
Septage & Sludge
Recirculate
Recirculate
Landfill
Landfill
Landfill Leachate
Or
Landfill Leachate
Lagoons
(Anaerobic/Aerobic)
Lagoons
(Anaerobic/Aerobic)
Solids
Disposal
(Landfill)
Liquid
Disposal
(Deep Well)
Caribbean Case Study - Barbados
Current situation:
• 9,000 m3 /day secondary wastewater
treatment system at Bridgetown, producing
primary and secondary sludges which are
land spread.
• 9,000 m3/day advanced preliminary treatment
plant for the South Coast, producing ~ 750
kg /day of screenings, currently bagged and
landfilled. In-situ incineration is planned, at
an estimated capital cost of ~ US$1.0 million.
Barbados Case Study Continued
• New engineered sanitary landfill (1.0 m of compacted
clay liner) at Greenland with leachate collection and
treatment capacity (anaerobic, facultative and
aerobic lagoons in series). Built in 1997. Not yet in
use.
• Current landfill at Mangrove being extended, with
new cell having a composite liner and leachate
collection system. However, leachate is currently
being recirculated onto a section of the landfill that
is not lined.
• Special wastes (abattoir wastes, grease) currently
being land spread at another location.
Too Many Cooks?
• In Barbados, the administration of waste
management includes the following agencies:
• Design of new landfill – Sewerage & Solid Waste
Project (S&SWPU) Ministry of Health
• Design of Extension to old Landfill – Sanitation
Services Authority (SSA) Min. of Health
• Operation of old landfill – SSA
• Design and construction of the South Coast
Sewerage Project (SCSP) – S&SWPU
Too Many Cooks?
• Operation of the SCSP and the Bridgetown
WWTP – Barbados Water Authority – Ministry
of Utilities.
• Result: not only are different agencies
responsible for solid and liquid waste
management but different agencies are
responsible for design vs. operation. This is
typical in the Caribbean with a notable
exception being St. Vincent & the Grenadines
with the CWSA responsible for both solid
and liquid waste.
Recommended Synergistic Approach
• Dispose of residuals from the SCSP (screenings) by
bagging and landfilling and abandon the incineration
plan.
• Abandon the plan to build a separate mechanical
treatment septage and sludge handling facility.
Dispose of these residuals at the landfill and operate
the new cell at the existing landfill as a bioreactor.
• Special wastes (blood and grease) can be cocomposted with yard waste at the proposed national
composting facility or added to the liquid stream
recirculated to the bioreactor cell at the landfill.
Conclusion: Real World?
 Solutions can appear very simple on paper yet are
little more complicated to implement in the real
world
 On a daily basis, landfills, sewage treatment plants
and septage and sludge facilities throughout the
Caribbean continue to operate and generate
residuals
 The responsibility for cost effective business
practices rests on the shoulders of the General
Managers and the Directors of these operating
entities
Conclusion
 It can be concluded that there is merit in
investigating cooperative solutions that could
result in cost savings, a higher level of
environmental protection and reduced risk
 The benefits are numerous:
• Residuals from one stream could benefit another
system resulting in a useable end product
• Capital and operating costs could be reduced
• Risk of damage to the environment from the
mismanagement of these residuals could be
prevented
Thank you