give me a break - a windbreak

Give me a break! ………. A Windbreak that is.

An informal guide to Windbreaks as an odour amelioration technique

Is the stink getting a little too strong for the neighbours? Researchers have found that natural and artificial windbreaks can reduce the odour associated with outdoor manufacturing activities and processes

© Anotec Pty Ltd ◊ PO BOX 292 BOTANY NSW 1455 ◊ Tel: (02) 9700 1222 1

For an odour to be detected downwind, odorous compounds must be: (a) Formed, (b) Released to the atmosphere, and (c) Transported to the receptor site. These three steps provide the basis for most odour control. If any one of the steps is inhibited, the odour will diminish. Unfortunately many people "smell" with their eyes. Providing a natural or artificial barrier between facilities and the public eye can reduce the localized environmental impact of your facility’s operation, especially when it comes to odours. In order for odour emissions to be a nuisance in the community or neighbourhood the odours must drift offsite. As the odours move offsite with the ambient air the odour is diluted out. If enough ambient air is mixed with the odorous air the odour concentration is reduced to the point where the odour is not detected. Encouraging this dilution and dispersion of odours is the most basic technique for reducing nuisance odour problems. Unfortunately, the downwind movement and dilution or dispersion of airborne emissions from a leather tanning facility is difficult to predict and is affected by many factors including topography, weather, and building orientation. Increasing dispersion will impact the downwind concentrations of odours, gases and dust but will not impact the amount of these constituents. This is an important concept when regulatory concerns are being addressed. Dust

Dust is also a component of odour and may be the most detrimental because it can be transported long distances along air currents. Dust particles act as a transport mechanism for odour. Gases and compounds disperse but dust will carry compounds farther. Dust particles may also deposit next to olfactory cells where the odour can continue to affect a person. The dust can come from many sources, including dried sludge, raw materials and animal hair or skin.

Wind

Wind direction has a major impact on how odours travel. If considering the relocation of your lagoon – plan plan plan! Check the direction of prevailing winds and compare them with the direction toward neighbouring residences, public use areas, highways, population centres and also any areas to be developed in the future. If the summer prevailing wind is toward any such places, it would probably be best to choose another site. For example, if winds typically come from the northwest in winter and south to southwest in summer, then, the preferred


locations for lagoons are straight north or straight east of housing to minimise potential problems.

Distance

In addition to wind direction, distance is important. Odour intensity decreases as distance from the source increases. Distance allows fresh air to mix with the odours, resulting in decreased odour intensity. Separation distances are based on the odour source type and the size of the operation. As an estimate, suitable distances can range from 230 to 760 metres.

Mismanagement of lagoons can cause increased odours throughout the year. In addition to having enough dilution water, it is also important to release consistent amounts of wastewater frequently into the lagoon. This allows the bacterial population to stabilize and break down the waste as it is added. Adding too much waste at one time, or at infrequent intervals, causes a situation similar to the spring warm-up, when too much waste is available for decomposition at one time. This procedure really starts with proper sizing of the lagoon. If the lagoon is too small, a similar effect is seen as adding too much waste at one time or not having enough dilution water. The lagoon must be large enough for adequate dilution of the waste added to have proper decomposition without excessive odour production. Operations that add production facilities that release solid waste into a previously constructed lagoon may be asking for trouble if the lagoon is not large enough to properly break down the additional waste. An important aspect of proper lagoon start-up is that adequate water be in the lagoon before any manure is added. The lagoon should have to of the minimum design level to ensure adequate waste dilution to properly start the degradation process. Lagoons should also be started during warm weather when bacteria are more active.

The solids' component of tannery waste is of primary interest in lagoon function because the solids' component contains the organic matter that is broken down by bacteria. Therefore, the solids are ultimately the source of odours. If the amount of solids released into a lagoon is reduced, odour production should also lessen. One method of reducing the solids in a lagoon is to separate the solids from liquids before the liquids are released into the lagoon. There are a number of processes by which this can be done, including mechanical processes or simply gravity in a settling basin or tank.

But first, some other possible solutions to lagoon odours.

Odours can become a problem when wind blows across any liquid surface and odours are allowed to escape from the site. This is especially a concern with lagoons, which have large surface areas exposed to the atmosphere, thus allowing plenty of opportunity for odour release.


One method of reducing the odour escape is to cover the lagoon/tank/dam. This is easier done with some structures than others. Concrete structures may actually be capped, so the structure is totally enclosed. Other structures may be covered with materials such as large tarps. Another product is an oil based film that spreads over the entire surface. The key to success of this process is to decrease the interaction of the liquid surface with the atmosphere. To be effective the cover must maintain coverage of the liquid surface in order to decrease the chance of the atmosphere picking up odours and spreading them.

A similar concept is a floating biological cover. One example of such a material is a layer of straw. The bio-cover reduces interaction between the liquid surface and the atmosphere. One problem with floating bio-covers is that they will sink after a while and therefore must be replaced. One possible solution that has been suggested is to add mineral oil to the biological material as it is blown out on the surface. Of course, there is limited information regarding tannery lagoons so Anotec have applied information regarding waste lagoons to this document.

Some products are designed to cover up or offset the odours that have been released into the atmosphere.

Masking agents are one class of products that have an odour that is stronger than the odour from the lagoon. The object is to cover the odour with a stronger, hopefully less offensive, odour.

Another class of products is counteractant, which work by offsetting the malodours with another odour so that the two odours basically cancel out one another, thereby reducing odour intensity. One difficulty experienced with counteractant is knowing what odour to offset. With the great variation of odours possible, it is difficult to know which odour to prepare for and thus what product to use. In the past success of this type of product has been variable and somewhat limited, hence Anotec’s inclusion of sensory and analytical methodologies in identifying the odour thus formulating the most appropriate counteractant. A third class of additives is deodorants. These products are to eliminate odour from the site, either by preventing the escape of specific gases or by killing the organisms that cause the odour. Enzymatic products are a fourth class of additives. These products are supposed to alter the biological pathways involved in waste decomposition. As with many of the other classes of additives, success has been erratic and there is limited data. Much work is currently being conducted at a number of universities to evaluate many different products and the effectiveness of each at reducing odours, and under which conditions the products work best.

One treatment method that does reduce odour if conducted appropriately is aerobic treatment. This process involves adding enough oxygen to the waste so that the aerobic bacteria can live and break down the waste material. The products of aerobic digestion are generally carbon dioxide and water, two compounds without much odour. One major concern with this method is the need to be sure


adequate oxygen is added. There are several procedures available or being developed to accomplish this. One method is to install a surface aerator that incorporates air into the waste material, either with windmills or electric motor driven aerators. A second method is to release oxygen into the waste. There are a number of ways being developed to do this, including bubbling oxygen below the sludge surface. A second major concern with aerobic treatment is the cost required to apply the treatment. The process does work if conducted properly, but it is an expensive alternative. Another speculation is to combine both surface aeration and bacterial additives to control odour.

What the @#$% is a Windbreak? Windbreak walls are an odour reduction technology used quite frequently where walls made of plastics, tarps, and plant residues are erected downwind from various odour sources such as lagoons, ponds, waste storage areas and exhaust from buildings. In other words, windbreak walls are a type of wall that deflects malodorous air upward from lagoon, pond or waste storage areas so it mixes with clean air, which dilutes odours and gases. The lesser the air movement over and around wastewater treatment areas will mean the lesser mixing of unpleasant smells. Windbreaks properly located around your lagoon, dam, pond or solid waste storage area should help to deliver much cleaner air to all downwind noses.

Hopefully, what once was a waft should be only a whiff.

The Windbreak It’s the wind that carries unpleasant odours from manufacturing facilities and outdoor treatment sites to neighbouring noses. So the question is: “Could a windbreak help to control odours from leather tanning facilities?” The answer is yes.


Although unpleasant odours will not be completely stopped, a properly designed windbreak located upwind of the wastewater treatment or lagoon/dam area should help to reduce the movement of odours. A windbreak will reduce the amount of air that moves past the dams. Strong winds will be slowed and calmed by the erected barrier. Excessively turbulent winds will be diverted up and over the affected area/s. Windbreaks serve to reduce the amount and the intensity of air that mixes with the smells. Less moving air means less movement of odour. However, wind direction changes. To guarantee that windbreak protection will always be located upwind from the affected area/s, windbreaks can be built or, in the case of using natural windbreaks, planted around as much of the perimeter of the lagoon as possible. An opening in the windbreak to enable access to the waste treatment area should give you lots of manoeuvring room for the largest machinery. Windbreak walls help to disperse odour and provide a means for controlling odour and dust emissions between the source and the receiver

There are five primary ways that windbreaks can reduce odours.

Windbreaks create turbulence as the wind moves through, over and around the structure diluting gas concentrations of odours.

Lowering wind speeds over lagoons can reduce release of odour. Windbreaks can reduce wind speed up to 90% which allows dust and aerosols to settle out of the air.

Trees are effective in combing particles of all sizes out twenty-fold better than bare soil.

Researchers have found measurable quantities of Volatile Organic Compounds upon and within plant tissues. Trees act as a sink for VOCs.

Build or plant a windbreak on windward side of lagoons to reduce wind speed and the release of odorous compounds.

A properly designed windbreak should allow about 35 to 50 % of the wind to pass through it but at a much slower and more even speed. The other 50 to 65% of the wind will be pushed up and over the windbreak and, most important, up and over the affected areas. Some wind must be allowed to flow through the windbreak. Wind that flows through a planted windbreak such as trees acts like a cushioning pillow (air pressure) that holds the faster more turbulent wind aloft. The fast turbulent wind remains aloft, gradually returning to the ground, for a downwind distance that is equal to about 15 times the height of the windbreak; for example, a 6 metre high windbreak will provide about 90 metres of downwind protection.


If the windbreak is too thick and dense e.g. thick wood, the cushioning air pressure will not form downwind of the windbreak. The turbulent air will be drawn down very quickly becoming even more turbulent causing excessive mixing of the offensive odour into the air.

Windbreak walls can be constructed of various materials such as metal, straw, or wood. Without a wall, exhaust air moves along the ground and is not diluted. A windbreak wall helps to direct odorous air travelling over the lagoons upward for better dispersion/dilution. The cost of a windbreak wall can vary depending on the materials used to construct the wall, which can in turn vary from hay bales to concrete blocks to a frame supporting polyurethane or similar sheeting. A small note on hydrogen sulfide H2S is heavier than air so it accumulates in pits and other low lying, unventilated areas. Hydrogen sulfide concentrations should not be high enough to cause concern as you move away from the lagoon, pond or waste storage area. Potential role of Windbreaks There are four primary ways that windbreaks can ameliorate lagoon odours:

1. Dilution of gas concentrations of odour into the lower atmosphere 2. Encouraging dust and other aerosol deposition to the windward and lee

sides of the break by reducing wind speeds 3. Physical interception of dust and other aerosols 4. By way of acting as a sink for the chemical constituents of the odorous

pollution Pollution Dilution Depending on the current climatic conditions, odorous aerosols and gases can travel significant distances. The conditions leading to pollutant trapping by the atmosphere are well known. Temperature inversions can create this situation as the inversion can restrict air mixing into the lower atmosphere. Atmospheric inversions, where the normal temperature structure of the atmosphere is reversed, that is temperature increases with height rather than decreases, result is stable atmospheric layers which play significant roles in the extent and effects of odour plumes.


High concentrations of pollution can occur at ground level as a result of ground-based inversions preventing or limiting vertical mixing or atmospheric layers. Low wind velocity and lack of physical landscape features that create turbulence can also contribute to pollutants being trapped in the atmosphere. As wind speeds decrease, there is less turbulence, and therefore less dilution of escaping odours. The odour problem has a tendency to be most severe during stable, night-time conditions with low to moderate wind speeds, at which times odours emitted near the surface will not diffuse upward but remain near the surface and travel by way of near laminar flow that will meander over the terrain. Air temperature is also a major factor. At higher temperatures, the conditions for anaerobic decomposition can improve, and greater volatility of odorous compounds may occur. When these weather conditions occur singly or simultaneously, odour has been noted to be transported to distances greater than 3 kilometres. Windbreaks have the ability to lift some of the plume constituents into the lower atmosphere aiding in the dilution and dispersion process. As studies in the distribution of windblown pollution indicate, the properties of the underlying surface (terrain) is important in deflecting the airstream or in modifying the rate of mixing and consequent dilution of the material carried with it. Windbreaks present an obstacle to the wind, deflecting air streams upward. As the air streams top the obstacle, the stream is redirected, compressed and air speeds increase. This effected zone above the windbreaks has been noted at heights of 1.5 H (that is 1.5 times the height of the barrier) to 1.7 H. This zone then widens and follows the air stream downwind and acts as a source of turbulent kinetic energy. In studies that have modelled the dynamics behind artificial windbreak fences, a “quiet” zone that extends from the top of the barrier down to a distance of about 8 H from the barrier exists. Outside this quiet zone the longitudinal turbulent fluctuations are more energetic and larger in scale. It is in this zone, depending upon the height of the windbreak, that much of the dilution of the odour plume may take place. Porosity is of particular importance, in terms of turbulence, as windbreak porosities of < 40 % are associated with the greatest amount of turbulent energy transfer. Recent studies conducted in the U.S. indicates that artificial wind break walls can deflect malodorous air so that air flows higher above the ground or the surface of downwind lagoons improving potential dilution of odours to the point of noticeable positive odour reduction downwind. Dilution is important to reduce odorous gas concentration (which is the concentration of the odorous gas relative to the concentration at the threshold of detection as determined by olfactometry). Dilution to the point where it will not be considered, to some degree an on-site nuisance, and to a large degree an off-site, downwind nuisance is critical.


Dispersion as a control strategy involves using the natural turbulent mixing of the lower atmosphere to reduce concentrations emitted by an odour source to acceptable levels before the emissions reach a critical receptor such as humans capable of sensing an objectionable odour. Previous research studies have shown that odours were stronger downwind of an odour source without the windbreak wall and inside the windbreak wall enclosure, than odours on the far side of a lagoon or 3 meters downwind of the windbreak wall. Despite these studies, the mechanism for the odour reduction (increased dust deposition or increased atmospheric dilution) remains to be identified and fully quantified. The difficulty in determining the effectiveness of windbreak walls or windbreaks on odour control has been noted by several researchers. This difficulty is due to three notable factors.

1. The first factor being the inherent difficulty in measuring complete wind directions in the field and in ventilated air.

2. The second factor is in separating the source of odour, for example odours emitted from lagoons often complicate measurements in downwind odour reduction.

3. The third factor involves the difficulty in measuring boundary layer/ turbulence effects from porous objects.

Windbreaks present an obstacle to the wind, deflecting and lifting air streams (odour plumes) upward into the lower atmosphere. The lifting aspect will begin at some distance on the windward side, typically a distance equal to 2 to 5 times the height (referred to as 2 –5 H) of the windbreak. Liquid Application Depending on the dimensions of the land, multiple windbreaks could be used on both sides of the field, orientated perpendicular to prevailing winds, for diversity of effects. A windbreak on the windward side of the field could be used to capture off-field particulates that would otherwise pass over the field surface and pick up VOC’s being emitted. This would also encourage particulate deposition. A windbreak on the far side should create turbulence and enhance odour dilution as well as interception and encourage deposition of some particulates. Windbreak density should be increased for maximum turbulence (< 60% porosity). To maximize turbulence wind speed needs to be at its prevailing rate, so if a two rowed system is used, the field should to be wide enough to allow for the wind speed to regain its prevailing velocity as it approaches the turbulence creating belt.


Windbreak height is also an important variable for dilution. Taller barriers or structures would be recommended Some studies have indicated that placing windbreaks around lagoon or storage structure perimeters can reduce wind flow at the liquid level and therefore reducing convection of VOC’s from the storage surface may prove effective in odor reduction. Numerical simulation of the effects of tall barriers around lagoons predicted reductions in downwind malodorous lagoon emissions of 26% to 92%. Lowering wind speeds over lagoons can reduce convection of odorous compounds from the surface and allow for slower release of the odour plume which also facilitates dilution. Summary

Windbreak barriers reduce ground-level wind speeds

Windbreak barriers reduce emission of odours from lagoons by reducing wind speeds over the water body.

Airflow past windbreaks have more turbulent air mixing

Let’s show you what we mean


The Situation

A windbreak slows the wind in one place by deflecting it to another. The best windbreaks produce a zone behind the windbreak which will have wind of about a quarter of the speed. For a 15 metre high windbreak this zone will extend about 76 metres downwind. From 76 metres to 152 metres the wind speed will increase up to about half that of the incoming wind. Beyond that wind speeds increase quickly.

An Analogy

The wind is like a river, with the earth equivalent to the bottom of the river. Water flows and tumbles over the river bottom. The faster the flow, the more tumbling that takes place (turbulence).

If we were to throw a large rock into the river, we would create a sheltered spot immediately behind the rock. This is a windbreak in its most basic form. The problem is that just past the rock, the water that had been deflected over and around the rock would come crashing down and in.

The Windbreak

Windbreaks control the amount of "crashing down and in" by letting a little wind flow through. The wind flowing through holds the faster (deflected) wind away for a few hundred metres. This lets the winds merge together again more gently with less turbulence.

The following pages show in diagrams what a windbreak does, so, now for the pictures:


A Simplistic View (a) Without a windbreak barrier (b) With a windbreak barrier between residences and lagoon (c ) With a windbreak barrier BEFORE wind reaches lagoon. Odours will be minimised but still perceptible.


(d) Double windbreak barrier

Wind direction

lagoon

houses

Taller windbreak

Of course this is just a simplified (not drawn to scale) depiction of what may happen when a windbreak barrier is installed. In some cases there are homes or neighbours on either side of the lagoon. In this instance (d) is the better option when designing your shelterbelt or windbreak.


Using natural windbreaks A natural windbreak (aerial view of a UK farm)


Windbreak Design Different types and colours For shade cloth are available (make sure it’s commercial Grade)

Simple construction (small scale)

© Anotec Pty Ltd ◊ PO BOX 292 BOTANY NS

Windbreak design using posts. Suggested and example only: Treated timber posts are embedded 1.2metres in the ground. 3.6 metres above ground (5 metre length)

- 3.6 m centres for 15 cm posts - 900 mm centres for 10 cm posts

High quality plastic eg. 40 mil medium densitypolyethylene which is nailed to post. Note: there are any types of materialavailable for use including high densitymeshes.

W 1455 ◊ Tel: (02) 9700 1222 15

FAQ

Q. When is it important to avoid hilltops when designing a lagoon?

A. Odour will travel downhill with air currents and humidity. When residences are in valleys below a waste treatment or sludge storage site they receive more odour emissions. However, hilltops are a good site for naturally ventilated buildings. These factors should be balanced.

Q. How do windbreaks around lagoons decrease odour complaints?

Windbreaks shield the site from public view. It is believed that there is an "out of sight, out of mind" factor that affects the level of complaints. Windbreaks also lift air currents. This has two potential impacts.

1. If the windbreak is upwind from the facility’s site, air currents are lifted prior to picking up odorous compounds and dust so the odour potential is diminished.

2. If the windbreak is between the facility’s site and neighbouring residences, air currents are lifted and stirred, making the odour plume to dissipate more rapidly.

Q. Explain why excessive odours are released from lagoons during spring warm-up?

A. Biological activity is low all winter in lagoons during cold temperatures. When temperatures increase, the activity increases. Because the lagoon has been biologically overloaded all winter it takes the microbes time to catch up to the loading rate and regain equilibrium. Therefore, the lagoon will stink during this process.

Q. What are some lagoon management activities that can decrease odour generation and release?

A. These guidelines will help to keep lagoons from producing many odours:

-maintain consistent and frequent loading of the lagoon

-add the proper amount of dilution water

-start the lagoon during warm weather


-initially fill the lagoon ½ to 1/3 with water.

Q. Why is morning the best time of day to apply sludge in land applications?

A. Air will generally be warming in the morning and thereby lifting odours for better dispersion. This will also promote drying of the solids. In the evening, humidity will make odours settle into low places and cause the odours to "hang" in the air longer.

Q. What are some available products that claim to counteract odours?

A. Several categories of products are available. These categories are:

-Masking agents - to cover odours

-Counteractants to "cancel out" odours

-Deodorants to eliminate certain gaseous products

-Enzymatic products alter the biological activity.

It is vitally important to make sure products have been tested by a reliable laboratory before accepting odour-reducing claims.


Final Important Note: Windbreak barriers will decrease the speed and divert airflow but may not reduce emissions. This form of “odour control” can be classed as a preliminary treatment to form part of a hybrid system. Anotec are currently designing and formulating such a system that will, once installed and assessed, significantly reduce the impact of odours onto the community. Example of an Anotec system:

Fencing to be placed around the residential side of the lagoon

Approximate height 2.2 – 3.0 metres high

Here, the windbreak is diverting the malodorous emission upwards. An Anotec system (portable type) is positioned along the windbreak or lagoon to intercept and significantly reduce the odour intensity as it travels upwards and onwards.


OPTION 1: Odour control along the windbreak

Windbreak


30 metre windbreak

15 metre spray dispersion

OPTION 2: Direct fogging of lagoon

Theoretically, the portable units will create a “blanket” of odour control fog over the lagoon

Wind direction

give me a break - a windbreak

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