Presentations

Angus Marland, Ameco Ltd.UK
 
 

Living Machines
 

Living Machines consist of a number of ecologically engineered components which are combined to form a complete treatment system.  For sewage treatment, the most efficient configuration for treatment to advanced wastewater treatment standards is:

 * Headworks
 * Anaerobic primary treatment
 * Aerobic reactors
 * Clarifiers
 * Ecological Fluidized Beds, and/or
 * Constructed wetlands
 * Discharge works.

The  implementation process for a typical Living Machine project involves four key stages

 * Initial discussions and site visit
 * Outline proposal and budget estimate
 * Preliminary engineering report 
 * Detailed engineering and subsequent construction.

* Living Machines treat municipal and industrial waste water to advanced, tertiary standards, enabling water to be recycled for non-potable uses or discharged directly to the environment.  This results in minimal charges for disposal of treated water to sewer.

* Lower capital and operating costs than conventional alternatives for waste streams requiring treatment to re-use standards.

* Mechanically simple and biologically complex, and therefore resistant to drastic changes or ‘shocks’ to the waste stream.  This provides high reliability and compliance to discharge consents.

* Little or no chemicals are used and there is significant reduction in energy consumption when compared with conventional processes.

* Generate energy when high strength waste is treated in a n anaerobic reactor to produce methane.

* Sludge generation is significantly lower than alternative technologies.  In Living Machines, sludge is utilised as a food for elements of the ecosystem and therefore the majority is consumed before removal is required.  Further sludge digestion in reedbeds provides inexpensive on-site treatment.

* Living Machines are beautiful by nature and environmentally restorative by function.  Owners of Living Machines often take advantage of this to show the facility as an indication of their environmental responsibility. 

* They can provide valuable by-products - plants and fish. However, extensive research is needed to assess the extent of pollutant accumulation in these by-products

Reedbeds and Constructed Wetlands

Reedbeds and Constructed Wetlands are man-made systems which simulate the water purification which has been observed to take place when polluted water is led into naturally-occurring wetlands.  They consist of saturated substrates, emergent and submergent vegetation and water that simulate natural wetlands.

Wetlands commonly include the following five principal components:

•  Substrates with different rates of hydraulic conductivity
•  Plants adapted to water-saturated anaerobic substrates
•  Invertebrates and vertebrates
•  Aerobic and Anaerobic microbial communities.

Horizontal Flow Reedbeds

In these systems, the wastewater is fed in at the inlet and flows slowly through the bed in a horizontal path until it reaches the outlet zone.  Here it is collected before leaving via the level control arrangement at the outlet.  During its passage, the wastewater will come into contact with a network of aerobic, anoxic and anaerobic zones.  Rhizomes grow vertically and horizontally, opening up the bed to provide hydraulic pathways.The most common plant used is the common reed (Phragmites australis).  This has the ability to transfer oxygen down through its leaf and stem structure, into rhizomes and out through the roots.  Bacterial populations proliferate in the area around the rhizomes.
 

Vertical Flow Reedbeds

These systems comprise a flat bed of gravel topped with sand, with reeds growing at similar densities to horizontal flow systems.  the liquid is fed onto the bed in a large batch, thus flooding the surface.  The liquid then gradually drains down through the bed and is collected by a drainage network at the base.  The bed drains completely free and this allows air to refill the bed.  the next dose of liquid traps this air, and this, together with the aeration caused by the rapid dosing onto the bed, leads to good oxygen transfer, and hence the ability to nitrify.

As with the horizontal-flow systems, the reeds will transfer some oxygen down to the rhizosphere, but is small in comparison to the oxygen transfer created by the dosing system.
 

Pond and Reedbed Systems 

Pond and Reedbed Systems are individually-designed, robust, and self-maintaining, and can treat domestic, municipal, agricultural and industrial waste water to very high standards. 

They consist of a series of shallow outdoor ponds, fringed with various species of emergent plants, and are linked by areas of aggregate-filled constructed wetland.  Systems can be built for as few as 5 people and as many as 3,000. 
Land requirements are approximately 10m2 per person equivalent, depending on conditions.

Performance

The overall hydraulic retention time is 30 days.  Shock loadings are buffered very effectively due to the long retention, and the resulting effluent has a consistent rating, with the ability to meet consents as low as <5mg/l BOD, <5mg/l TSS, <5mg/l NH3, <5mg/l total P.
 

Treatment Process

After screening and initial aeration, wastewater enters the first pond.  Aeration cascades maintain a circular flow in the pond, mixing, aerating and dispersing the influent thus preventing stagnation pockets.  During the day, algae and higher plants in the water generate large quantities of dissolved oxygen which sustains bacterial metabolism of the pollutants.  At night, aeration is provided by the cascades, to ensure that the surface layers of the pond remain aerobic.

Effluent is retained in the first pond for 15-20 days, and then flows into a constructed wetland planted with marsh plants, where further biological filtration takes place.  Reed roots provide an excellent aerobic habitat for microorganisms to degrade pollutants. 

This drains into a second pond where remaining biological pollutants are converted into biomass and any soluble nutrients are assimilated by algae.  The algal and bacterial biomass produced is constantly consumed by the lower animals in the community, which themselves serve as food for higher animals.  After passing through a second wetland, the effluent is polished in a final pond prior to discharge into the receiving water. 

Sustainable Urban Runoff Treatment

Surface water from roads, roofs and driveways drains into rivers, streams, ponds and other watercourses.  Until recently, it was often considered clean, but this runoff can contain high levels of suspended solids, hydrocarbons and heavy metals.  Industrial hard standing areas can also give rise to significant levels of contamination from cars, lorries, soil, spillage and cross connections.

Watershed Systems Ltd has designed and constructed surface water systems which implement the Best Management Practice (BMP) guidelines which are recommended by the Environment Agency and Scottish Environment Protection Agency.

The systems are designed to:

• Improve water quality by settling suspended solids and trapping hydrocarbons
• Attenuate storm flows to achieve green field runoff rates, preventing surges of polluted water entering and eroding streams
• Digest and fix pollutants through microbial activity
• Enhance wildlife and amenity value of a site
• Encourage infiltration to assist recharge of aquifers or groundwater.

Source control measures include grassed swales, gravel filters and other features designed to maximise infiltration such as porous paving and infiltration basins.  They may also include a series of balancing and treatment ponds and basins sized to incorporate passive treatment within landscape features.

In addition, water can be piped to a location for passive treatment through ponds, wetlands and reedbeds.

Site-specific solutions are often required, and a good design can enhance the wildlife and amenity status of an area.  Domestic property values can be increased by the inclusion of a water feature. 

Issues related to safety must be addressed and taken care of during the entire process of designing, execution and operation of Living Machines projects.