Urine as fertilizer: Maximizing hay yield and enriching low-N composts

Urine as fertilizer: Maximizing hay yield and enriching low-N composts

Summary

The Rich Earth Institute is pioneering the use of sanitized human urine as an innovative and sustainable fertilizer. Wide-scale reuse of urine as fertilizer would provide a stably-priced, locally produced, and sustainable source of fertilizer for farms, while directly alleviating the growing problem of nutrient pollution of surface waters by septic systems and wastewater treatment facilities.

This report focuses on activities conducted under an extension of the 2014 SARE award (ONE14-218) for the project titled “Urine as fertilizer: Maximizing hay yield and enriching low-N composts.” For details on our continuing research under a 2015 SARE award (ONE15-244) “Value-added products from urine: Enriched compost and stabilized liquid fertilizer” please see the annual report for that project.

However, for the purposes of this project, two experiments were involved:

1) determination of optimum dilution rates for urine application to hay, and
2) testing eight regimes for co-composting urine with various substrates.

Some of the relevant work reported in this document was performed above and beyond what was proposed and funded, and therefore cannot be specifically attributed to either the 2014 or the 2015 SARE project. For this reason, narrative describing some of these items appears in both reports.

A computer-controlled compost incubator was built for the study, capable of maintaining constant temperature and monitoring oxygen consumption and ammonia volatilization from four composting vessels. Four recipes of different solid feedstock mixed with urine were composted at 30°C. Two of the four recipes composted actively, while the other two suffered from low respiration rate and elevated pH.

The Rich Earth Institute developed a new, high-capacity, portable pasteurization system for recycling urine into fertilizer, and received a long-term state permit allowing it to produce and distribute urine-derived fertilizer for farmers to use without restriction.

In a related but separate project, the Institute continued EPA-funded field trials to assess the persistence of residual pharmaceuticals from urine-based fertilizers in vegetable crops, soil, and groundwater.

Objectives/Performance Targets

Processing:

We received a 10-year permit for a portable urine sanitization facility from the Vermont Department of Environmental Conservation on May 15, 2015. This allows us to process up to 500,000 gallons of urine per year, at participating farms or other facilities throughout the state. Construction of the new continuous-flow urine pasteurizer was completed in May, and it was used for all urine treatment in 2015.

Performance tests of the pasteurizer show it to be capable of processing 720 gallons of urine per day with a heat recovery rate of approximately 80%. Assuming an electricity cost of $0.15/kWh, the cost to pasteurize urine using this device is approximately 0.9 cents/gallon, or $9.00/1000 gallons.

Given time and funding, we will develop a third-generation pasteurizer for the 2016 season, with the goals of boosting efficiency, durability, and processing speed, while decreasing size and mechanical complexity. This will allow for more efficient urine processing and may result in a design that can be used in other urine recycling projects.

Field trials:

2015 field trials are described fully in the annual report for project ONE15-244.

Composting:

Bench-top composting trials were conducted in a custom-built incubator, built of 8” structural insulated panels with a capacity for four 20 L plastic vessels. Heating was provided by an low-intensity, high-surface-area electric resistance panel on the floor of the chamber, which was switched on and off by a computer controller based on feedback from a digital temperature probe inside the incubator.

Aeration and leachate removal were supplied independently to each vessel by a vacuum hose connected to an air pump capable of drawing 4.14 L/min. The pump was switched by the computer controller to provide an independent aeration rate to each of the four vessels determined by the duty cycle of the pump. Exhaust from each vessel was routed to a leachate/condensate trap and then through a 0.25 N solution of sulfuric acid to capture ammonia vapor for measurement by titration with NaOH. Finally, the air passed over an oxygen analyzer connected to the computer controller/logger to determine oxygen consumption rates.

The controller/logger recorded ambient and incubator temperature, the aeration rate of each vessel, and the oxygen level in the exhaust air from each vessel. It then adjusted the aeration rate of each vessel (by changing the pump duty cycle) to maintain oxygen levels in the exhaust at approximately 10%.

A trial of four compost recipes was initiated on 1/27/15. The solid portion of the recipes were as follows, based on dry weight:

1. 85% horse bedding and 15% softwood shavings
2. 70% horse bedding and 30% softwood shavings
3. 40% horse bedding and 70% softwood shavings
4. 100% shredded hardwood leaved

The solid materials were combined, and then urine was added to saturation. The four mixtures were then loaded into the compost vessels and placed into the incubator. Each vessel contained approximately 1 kg of dry matter.

As is apparent in Figures 1 & 2, all mixtures showed oxygen consumption rates indicative of an initial flush of activity in the first few days, followed by a decline beginning on Day 3 for the 40% manure mixture and Day 10 by the 85% manure mixture, with the others in between. The leaf mixture underwent the most rapid initial decomposition, with a brief peak in oxygen respiration rate of over 3g/hr. All mixtures showed a respiration jump on Day 14 (when compost was removed, weighed, sampled, and replaced, simulating a turning) although the increase shown by the 85% manure mixture was barely noticeable because the turing came just after it had begin a steep respiration drop. Conversely, a subsequent turning on Day 48 resulted in a respiration drop in all vessels. Addition of supplemental urine on Day 59 and Day 72 caused temporary spikes in respiration rate of all vessels.

The 40% manure mixture had the lowest respiration rate and exhibited a strong ammonia odor at the time of the first turning on Day 14, which continued throughout the study period. The 70% manure mixture had a slight ammonia odor at the first turning which disappeared afterward. Neither of the other two mixtures ever had a detectable ammonia odor.

Total ammonia lost from the vessels and captured in the sulfuric acid solution is shown in Figure 3. The highest losses come from the 40% manure mixture, despite the fact that the computer controller gave it the lowest aeration rate due to its low respiration rate. This is not surprising, given that it was the mixture that smelled most strongly of ammonia. Still, given that each mixture contained approximately 15 g of N from urine and no vessel lost more than 0.6 g, N losses were low, at about 4% or lower.

The pH of the urine used in this trial was 9.35. As was expected, leachate from all vessels had a lower pH than the original urine. The 40% manure mixture had only a slight effect on leachate pH, producing a leachate with a pH of 8.85 on Day 48, when the other mixtures were producing leachates with pH between 6.5 and 7.7.

500 mL of supplemental urine were added to each vessel on Day 59, in order to see if the resulting leachate would have a neutral pH, which would result in any volatile ammonia being converted into nonvolatile ammonium. The resulting leachate had pH values ranging from pH 6.8 to 7.8.

• Figure 1
• Figure 2
• Figure 3
• Figure 4

Accomplishments/Milestones

TIMELINE 2015:

March–May: Urine collection, transport, storage

• Urine donor community kick-off event April 10, 2015 held at the River Garden in Brattleboro featuring Get on the Bus Productions presenting “What do we do with our Poo.”
• Bought, configured, and tested a reverse osmosis machine for removing the water from urine to create a concentrated fertilizer product.
• Acquired ten year permit from VT Watershed Management on May 15th, for mobile urine pasteurizing unit.
• Completed spring pump-out route with Best Septic from 10 homes that are using 55 gallon barrels for collection.
• Filled existing farm tanks with urine.
• New mobile pasteurizing unit built and tested.

June–July: Urine treatment

• Additional urine collected, transported to farms, and treated.
• Improvements made to pasteurizer, based on operational experience.

August–October: Urine application

• Urine and chemical fertilizer applied at Whetstone Valley Farm on 8/10, after first cut of hay.
• Additional pasteurized urine applied to other hay fields at Whetstone Valley Farm 8/25 and 8/26.

November–December: Hay harvested, Fall Urine Application

• Completed fall home collection pump-out route 11/6/15 from 10 homes that are using 55 gallon barrels for collection.
• Cut (11/2/15), dried, baled (11/4/15), and weighed (11/7/15) at Whetstone Valley Farm.
• Total urine collected in 2015 over 5,000 gallons.
• Urine collection continues through the winter.

Still to be completed:

• Full statistical analysis of field trial results
• Bench-top compost trials
• Bin-scale compost trials

Impacts and Contributions/Outcomes

Compost:

The 85% manure and 100% leaf formulas had the lowest ammonia loss and exhibited the highest respiration rates, while the mixtures with the lowest manure content (and highest softwood shavings content) had the highest ammonia loss and lowest respiration. It appears that softwood shavings do not provide a very good substrate for mesophilic nitrification, which improves with the addition of manure or the use of a different substrate such as leaves.

At this point, 100% leaves or 85% manure/15% softwood shavings appear to be the best of the four urine co-composting recipes. Subsequent repetition of this trial at 50°C will provide additional information on the performance of the four recipes, which will determine the two recipes that will be used in the large bin-scale trials later in 2016. If any of the recipes perform well at bin scale, they will become options for assimilating the nutrients from urine into a standard and well-accepted product at a low cost, and adding value by increasing the fertilizer value of the resulting compost.

Pharmaceuticals:
In addition to the SARE-funded research, the Rich Earth Institute completed a second and final season of field trials funded by the EPA as part of a study to determine if any pretreatment of urine to remove residual pharmaceuticals is advisable before urine is used as a fertilizer. The study, which assesses the persistence of pharmaceutical residuals from urine in soil, crops, and groundwater, is being conducted in collaboration with partners at the University of Michigan, University at Buffalo, and Hampton Roads Sanitation District. The Institute grew lettuce and carrot crops in situ, amended with urine, struvite, and synthetic fertilizers. Samples of urine, soil, groundwater, and crop tissues are currently undergoing chemical and biological analysis at labs at the participating universities. Final research results will be available in 2016.

Media:

The Rich Earth Institute’s work continued to generate local, regional, and national media attention including:

• 10 minute video: Peecycling, University of Michigan, April 1, 2015
• Local Articles in the Brattleboro Reformer and  The Commons
• National articles in USA Today (from Burlington Free Press), The Guardian, and The Boston Globe

Outreach:

• Institute staff travelled to Montpelier, Vermont twice in the spring to testify to meetings of the Fish, Wildlife and Water Resources Committee, the Agriculture and Forest Products Committee, and the Windham County legislative delegation.
• Kenya – Managing Director Kim Nace travelled to Nairobi where she presented Rich Earth Institute’s progress and findings to NGO project staff at Sanergy and other NGO projects, USAID, and World Bank sanitation leaders.
• Invited and sponsored by colleagues from Recode in Oregon, Research Director Abe Noe-Hays attended both the International Dry Toilet Conference in Finland and World Water Week conference in Sweden in August and September. His three week itinerary in three countries included meetings and interviews with key stakeholders in the emerging field of urine diversion and ecological sanitation, and site visits to pilot projects.

Academic/Industry Presentations:

• NOFA/Mass conference presentation, 1/10/2015
• Northeast Sustainable Energy Alliance (NESEA) annual conference in Boston in March. Directors of the Institute presented in a 2-session panel workshop titled “Rethinking the Urban Water Grid.”
• University of Michigan, 4/1/2015, Rich Earth Institute Directors presented their work to a graduate student seminar, and assisted colleagues from the EPA-funded pharmaceutical study in initiating urine collection on campus.
• WEFTEC (Water Environment Federation’s Annual Technical Exhibition and Conference) in September in Chicago. Abe Noe-Hays, Research Director, presented at this conference.
• University of Vermont – 10/30/2015 Directors presented to students at the School of Agriculture Friday seminar series.

In November, 2015, the Institute launched a new website.

Collaborators: