Permaculture Solution for Leachate Control in Community Composting System?

I help run a community composting program in my city and we have run into a few challenges that I hope to explore in the forums here.

One of these challenges involves leachate from our bins: our current processing hub is located in a small parking lot on asphalt and occasionally, usually due to an increase in rainfall, there is a rise in leachate runoff. It will run from the bottom of the bins (which are raised off the ground) into a few different streams and pool. Typically, we use our excess feedstocks (namely, wood chips) to surround the bins and absorb leachate. Over the past two years, this has created a small amount of soil atop the asphalt. We do not always have excess feedstocks to utilize in this way, as the bins take priority.

The issue comes with our neighbors. They are not happy about the odors that come from a buildup of leachate. We rent a few parking spaces to our neighbors and we operate a community garden that lies just beyond the bins, so this space is heavily shared. We own the whole lot and have some flexibility in making changes.

One of our first thoughts is to remove a large strip of asphalt in front of the bins and create a drainage system. This requires certain resources that we do have, but are difficult to enable at this time. With the right system—including permaculture elements—this newly opened patch of land could become healthy soil and used for the continued greening of our lot.

But if we cannot remove the asphalt, I do not have a secondary plan. I have been told that the main reason we keep our bins on asphalt is to reduce rodent habitation; we have rats in the community garden and have made many efforts to mitigate the issue for participants. I understand the logic of keeping bins on non-permeable surfaces for this reason, but I imagine there are much better ways to do it. I will explore the rodent issue in another thread.

Are there any ideas for controlling leachate runoff in these circumstances? Ideally our whole system would be reworked, but this is where we have arrived. I will attach a photo of some of the bins to help visualize our situation.

Can you incorporate IBC containers for the bottom of the compost bin Perhaps this would give an additional bonus of compost tea that could be recovered? Screened soffit vents for air circulation in the IBC sides if needed. Easily transportable with a forklift, rigid exterior frame. Access panels could be easily installed for both adding and removing finished compost. The IBC's are not attractive but they could be trimmed with fencing material to make them less obtrusive. I guess after posting and looking about this idea isn't anything new. However they do have containment stands that take in spills maybe incorporating one of those below your current bins would address the leachate issue.

Robert Ray wrote:Can you incorporate IBC containers for the bottom of the compost bin Perhaps this would give an additional bonus of compost tea that could be recovered? Screened soffit vents for air circulation in the IBC sides if needed. Easily transportable with a forklift, rigid exterior frame. Access panels could be easily installed for both adding and removing finished compost. The IBC's are not attractive but they could be trimmed with fencing material to make them less obtrusive. I guess after posting and looking about this idea isn't anything new. However they do have containment stands that take in spills maybe incorporating one of those below your current bins would address the leachate issue.

I think the idea of containment, creating a reservoir for the leachate, could be useful in future bins that we create. Thank you for the response!

In this situation, I do not think it is worth making any major changes to the bins themselves until we are going to entirely replace them with updated ones. We may do just that eventually, but it is not within our bandwidth right now. The front face is made of removable plastic planks, for working the compost at certain points. We would probably have to make some significant changes to the structure if we were to incorporate containment for leachate; I imagine the container would be in a separate compartment of the structure as to not disrupt the processing of our compost.

As I understand it, leachate and compost tea are not applicable in the same ways. I would think the smell indicates that there is primarily anaerobic bacteria present, and there may potentially be pathogenic bacteria as well. This would not be good for anything edible, though it may be useful for introducing nutrients and other organic material to non-edible planting areas if diluted properly.

It might help to add that all of these bins are full at the moment and we have eight of them at this site. Our team is very small and we need a solution that can be created with relative ease.

Some aerate when creating compost tea, the addition of aeration into a collection vessel might be a idea to look at.

If we were to move forward with removing a strip of asphalt in front of the bins and create a drainage system, what would be an effective way to layer that system? We would have two primary goals here: control the leachate runoff/odor and utilize it for remediating soil beneath the lot as much as possible. Ideally, this system would include greening of the strip with any species that may be beneficial to the community garden.

In Oregon anytime a leachate is being introduced to the groundwater big alarms and flashing lights come on. Though the idea of a lush green apron to the front of the containers sound appealing an apron to the rear might be a good idea, many Nitrogen accumulating plants  like alfalfa and rhubarb would create an obstacle if they were on the input side.

If you are getting leachate despite covered bins, is it due to standing backed up water from the pavement? Is the storm drain clear? Has the wood chip solution or something else clogged it? I like the other ideas above, and I generally would embed my compost in and above any garden I can, with soil contact so that leachate is absorbed by roots. It occurs to me mints might do fine in your shallow soil on the asphalt, and would turn the smell problem around to something pleasant.

Robert Ray wrote:In Oregon anytime a leachate is being introduced to the groundwater big alarms and flashing lights come on. Though the idea of a lush green apron to the front of the containers sound appealing an apron to the rear might be a good idea, many Nitrogen accumulating plants  like alfalfa and rhubarb would create an obstacle if they were on the input side.

Can you explain to me why compost leachate making its way to groundwater would be alarming? Would filtration through soil not be enough to remove potentially harmful contents?

To clarify, by "drainage system" I do not mean a channel that directs the leachate toward another collection area like a storm drain.

I think I understand how an apron to the rear might be preferable, but to confirm: are you saying that nitrogen accumulating plants like alfalfa and rhubarb would create an obstacle for the leachate to move through? The input side meaning the side that receives the input of leachate?

Thank you for addressing my questions and exploring this with me!

The leachate, depending on quantity would be nitrate rich and raises red flags, think stockyard, even though your input is much or would be much smaller. The taller plants that I suggest as a nitrate scavenger are taller and might make a barrier to access to a feed chute.  A trough of wood chips with the plants would in all probability would help with odors.

Ben Zumeta wrote:If you are getting leachate despite covered bins, is it due to standing backed up water from the pavement? Is the storm drain clear? Has the wood chip solution or something else clogged it? I like the other ideas above, and I generally would embed my compost in and above any garden I can, with soil contact so that leachate is absorbed by roots. It occurs to me mints might do fine in your shallow soil on the asphalt, and would turn the smell problem around to something pleasant.

It is not from standing backed up water; it seems to fluctuate based on the moisture level of the bins. For example, we see a significant increase in leachate when adding food scraps to the bins, after heavy rainfall, etc. If it helps, we currently use a ratio of food scraps, leaves, and wood chips, roughly 1:1:1.5. So there is no clogging. The leachate pools in the lot because it is uneven and there is no drain in the immediate vicinity of our bins. They are lifted on pallet-like structures and the leachate drips through the bottom.

I think that soil contact would be ideal, however the bins themselves will remain on asphalt at this hub. We are exploring various permeable pavers for our next hub, something less permanent that allows the leachate to pass through and reach the soil below. A great challenge comes from working with other communities/organizations/spaces/neighbors; we must respect and consider all input from the people we work with and sometimes this means compromising on our end (ie. compost bins that do not make contact with the ground). Eventually, we will have a much larger facility and full control over our operation, although these localized hubs will always be a part of our program.

I love the idea of planting mint in the shallow soil—it could be a very quick and effective solution! I imagine the mint would do well absorbing any excess leachate. Do you have any other plant recommendations for the shallow soil around these bins?

Mints are an excellent nitrate sponge.

I would start with why you have so much liquid coming out of the bin to begin with, rainfall shouldn't be able to get into the bin so should have no bearing on the amount of liquid coming out of them. On the point on draining it, that's a lot of compost and a lot of nutrients in one spot soil will not be able to cope with such a huge input, you would need some form of filtration system.  what comes out of the compost heap reflects what is going on inside, if you are getting a lot of stinky foul liquid coming out then the inside of that compost will also be wet stinky and foul. The excess liquid and the fact that is smells to me suggests that you have to many greens and not enough browns going in. Or I would guess in this case to many kitchen scraps and not enough paper/card/straw etc.

Robert Ray wrote:The leachate, depending on quantity would be nitrate rich and raises red flags, think stockyard, even though your input is much or would be much smaller. The taller plants that I suggest as a nitrate scavenger are taller and might make a barrier to access to a feed chute.  A trough of wood chips with the plants would in all probability would help with odors.

Excellent, I appreciate the explanation! I am wondering if there might be any particularly strong nitrate scavenger cover crops that would work in front of the bins, perhaps even in the shallow soil that is being built above the asphalt. In that case, we can continue to build soil atop the asphalt with very little additional labor.

Edit:

Robert Ray wrote:Mints are an excellent nitrate sponge

Well that answers that!

I understand what you mean about compromising in community projects, often with folks who don’t know what they are talking about or don’t seem to think they need reasons for their opinions. I have been a food forest site developer and manager for years, working with locals, tribes, schools, non profits and farmers. Almost all have been great, but those few that turn our water off or on randomly, mow our young trees (school district maintenance guys), spray roundup on parking lots upstream (same dumbasses) cut fences for no reason (gates we unlocked ya damn methheads!), break into shipping containers full of tools to steal or vandalize (I’d give them the food I grow with those tools!), have made me decide to turn my focus back to my own property, where I can at least do what I want and actually mount some kind of defense.

Skandi Rogers wrote:I would start with why you have so much liquid coming out of the bin to begin with, rainfall shouldn't be able to get into the bin so should have no bearing on the amount of liquid coming out of them. On the point on draining it, that's a lot of compost and a lot of nutrients in one spot soil will not be able to cope with such a huge input, you would need some form of filtration system.  what comes out of the compost heap reflects what is going on inside, if you are getting a lot of stinky foul liquid coming out then the inside of that compost will also be wet stinky and foul. The excess liquid and the fact that is smells to me suggests that you have to many greens and not enough browns going in. Or I would guess in this case to many kitchen scraps and not enough paper/card/straw etc.

The increase in leachate is not an especially frequent occurrence; it is something that happens once in a while, but the neighbors are very sensitive to it and have deemed it an issue. For the most part, our bins are well balanced. Many different people contribute to our program, including the occasional volunteer or youth group. We try to maintain the system as best as we can, but it is certainly difficult with such a small team and many wild cards thrown into the mix.

Indeed, the bins do not smell foul inside at all with one exception: we are a community compost collection program and, at the moment, have a stock of food scraps that sits in separate bins for an undetermined amount of time, depending on our participants' weekly output and our limited capacity. So when these rotting scraps go into the bin after sitting for a week or two, there is an odor. However, it is quickly mitigated through composting. Our processing bins smell like sweet soil! The leachate that runs out the bottom and into the lot is what occasionally smells; perhaps the rainfall has influence because we have layered material around the bins to absorb leachate and the rain pulls certain contents out of this material as it move through..

It might serve us well to add more brown matter to our food scrap stock bins until they can be incorporated. Unfortunately, we do not have much control over what participants place inside of their bins. We can make suggestions, but that only goes so far. These individual bins (5 gallons) are generally picked up biweekly, so there will always be a period of time that food scraps are rotting away outside of our system and building odors.

You make a great point that "what comes out of the compost heap reflects what is going on inside." We always intend to tackle these sorts of issues at the bin first and foremost, but there are so many other factors in our particular case (mainly that there are just two of us running the processing side of the program with over 200 participants, and only as a part of other responsibilities).

Thank you for the clarification on the soil not being able to cope with such a huge input and a filtration system being needed in that situation!

Ben Zumeta wrote:I understand what you mean about compromising in community projects, often with folks who don’t know what they are talking about or don’t seem to think they need reasons for their opinions. I have been a food forest site developer and manager for years, working with locals, tribes, schools, non profits and farmers. Almost all have been great, but those few that turn our water off or on randomly, mow our young trees (school district maintenance guys), spray roundup on parking lots upstream (same dumbasses) cut fences for no reason (gates we unlocked ya damn methheads!), break into shipping containers full of tools to steal or vandalize (I’d give them the food I grow with those tools!), have made me decide to turn my focus back to my own property, where I can at least do what I want and actually mount some kind of defense.

Yes! The struggles in an attempt to push a city forward with more sustainable initiatives! It is very important work, I think, and the compromises feel worth it because they are better than the alternative of nothing being done to improve upon our unsustainable systems.

Yet I certainly cannot hide my excitement for the day I have some land of my own hehheh..

After a bit more research and consideration, I believe we will plant a variety of cover crops and scavenger crops around our bins.

I came across a helpful article that was related to this issue: Balancing the Soil Fertility Equation: Five Ways to Reduce Nitrogen Leaching

Using practices, such as cover cropping, that build soil organic matter helps to slow the release of nutrients so that they may be utilized by plants or soil organisms before being leached out of the root zone by irrigation or rain water... A study conducted in California coastal vegetable production showed that a winter cover crop of Merced rye reduced nitrate leaching by 70%. One experienced organic farmer uses an oat scavenger crop to absorb excess nitrogen in the winter. In Iowa, winter rye is commonly used. Mustards, grasses, legumes, or mixtures of these are typical winter covers, but the species of the cover crop isn’t as important as the crop’s ability to grow well in that location.

This article directly relates to agricultural production, but it contains many applicable points that I hadn't deeply considered. We were thinking about building a simple hoop house over the bins to keep them warmer as we move into winter; this in combination with nitrate scavengers and cover crops, in the shallow soil, might solve all our problems at once. It will mitigate the excess leachate and put it to use, create a more pleasant environment for the neighbors, become habitat for more organisms, introduce new species to the area, and improve our processing.

Does anyone have more input on what plants might work well for us? Again, there is a bit of shallow soil around the bins and deeper soil to the rear, where the physical obstacle of larger plants will not interfere with our work. We are in zone 6b with approximately 49 inches of rainfall each year. Ideally, we would build a hoop house in the coming weeks to enable planting in December; otherwise, it might make more sense to wait until spring for planting. In my search, good options seem to be mint, lemon balm, alfalfa, rhubarb, oats, winter rye, hairy vetch, and crimson clover. It would be wonderful to get some perennials behind the bins.

Another question: will these plants be safe to consume after they utilize the concentrated leachate?

I will greatly appreciate any additions to this list!

I would look into diagrams for bog or wetland gardens if you are allowed to do that on that concrete. If you really have say, I’d take a sledge to the pavement and at least crack it up, if not removing as much as possible, to create some drainage and help reduce Anaerobic conditions that are going to be your main cause of foul smells, which you mentioned being atop neighbors’ concerns. Otherwise gravel, pumice or used hydroton that is often free and easily flushed, could help either way, and the compost naturally mixing with sharp river sand or pumice/hydroton would make a good potting mix.

Ben Zumeta wrote:I would look into diagrams for bog or wetland gardens if you are allowed to do that on that concrete. If you really have say, I’d take a sledge to the pavement and at least crack it up, if not removing as much as possible, to create some drainage and help reduce Anaerobic conditions that are going to be your main cause of foul smells, which you mentioned being atop neighbors’ concerns. Otherwise gravel, pumice or used hydroton that is often free and easily flushed, could help either way, and the compost naturally mixing with sharp river sand or pumice/hydroton would make a good potting mix.

Treating the area as a wetland garden is an interesting idea, though I am not sure it remains wet enough perennially. I think it will be good to read more about wetland garden design; there may be elements that make sense to incorporate, especially in terms of plants. The wettest areas are where we do the majority of our work, so with any changes made, access to the bins must be the primary consideration.

Reducing anaerobic conditions seems to be the primary goal here. I am still wondering about an increase of drainage, especially at the immediate exterior of the bins. Thank you for the suggestions!

Composting in bins the way we are doing it is far from ideal; this conversation has brought up many great solutions and areas of exploration.