Integrated Byproduct Streams for Enhanced Viability of Combined Dairy Farm and Milk Processing Operations

Current Artisan Cheese Whey Disposal

Attributes of the creameries that participated:

• Range of sizes (lbs. of whey processed per year):

• Location of creameries per state they were located:

There were 4 main modes of whey management trends were observed

1. Agreement with farmer to pick up (n= 5)
2. Can feed to their own animals on farmstead operation (n = 4)
3. Compost/process on farm and use for fertilizer/irrigation (n = 4)
4. Pay to have it hauled off/put down drain (n=5)

Significant operational costs are associated with having the whey removed from the farm or relying on a municipality to process in their grey water system.  This mode was mainly observed in the larger creameries which had out grown their local farmers needs to feed their animals or were dealing with primarily acid whey which is less nutrient dense for animal feed. 

Operational costs per lbs. of whey processed were predicted with R²  = 0.73 using the line of best fit equation  (n=16): y = 8E-10x - 0.0001. The point at which costs become significant for a creamery to process their whey occurs between 850,000 and 2,000,000 lbs. of whey processed annually.  The first data point that we recorded impactful costs for a creamery were those that are processing at least 2,000,000 lbs. of whey per year (n=9).  Costs ranged from paying high start-up costs to install a biodigester on site to operationally paying to have whey removed to an alternative location.  Creameries that are processing less than 1,000,000 lbs. of whey are likely to have little to no costs associated with their whey management system (n=9). 

There are a range of unique situations that made it hard to observe mass correlations in costs, such as:

• Particular location of creamery with extremely stringent local waste water laws
• Use of public funds to supplement installation cost of novel management systems onto property
• Weather change resulting in switch of whey stream from being a waste center to being a desired animal food source in geographical areas of extended extreme drought
• Exclusively acid whey in waste stream at high operational volume
• Missing operational costs due to tracking challenges

Manure to Whey Ratio

During the 35-day incubation period, there were different rates of biogas production. Some samples produced 60 mL within 24 h while others took ≥10 days.  Also, some of the samples stopped producing any biogas after the first or second gas samplings.  These differences were considered to be an indication of

• how quickly bacteria in the starter adapted to their environment,
• stability of bacterial community in the samples, and
• predominance of gas-producing bacteria.

In general, anaerobic digestion was stable at up to 50% substitution of whey for manure with primarily production of methane as the combustible biogas. When 75% or 100% of the manure was replaced with whey, most samples produced hydrogen with very little (<10%) methane being produced.  There was also for a greater tendency for early cessation of biogas production.

Neutralizing the whey before digestion had no significant effect on whether methane or hydrogen was the predominant biogas. Composition of the biogas was fairly consistent during incubation  with no consistent trend observed other time.

When replacing 25% and 50% of manure with whey, methane was the dominant combustible biogas (99.95 and 99.35%, respectively). With 75 and 100% replacement, more often only hydrogen was produced. This difference in biogas composition was explained by the higher level of fermentable carbohydrate (lactose) in whey. After digestion, pH was significantly decreased when whey percent was increased to 75%. Mean pH values were 6.51, 6.50, 6.36 and 6.19 for mixtures containing 25, 50, 75 and 100% whey, respectively.

For a 210-cow dairy farm, with an average milk production of 80 lb per day and a similar manure production of 80 lb per day, the amount of milk that can be converted into cheese and the resultant whey combined with manure is dependent firstly on how much manure can be collected and used in the digester This depends on whether the cows are pasture grazed or kept in confined housing. If only 60% of the manure is applied directly to the fields by the animal then there is only 47,000 lb of manure per week available to the digester. Secondly, it depends on the ratio of whey that can be added to the digester with the manure. At a 25% substitution rate, this would allow processing of 16,000 lb of whey per week. This would be generated from conversion of 17,000 lb of milk per week into ~1,700 lb of cheese.

Economic Analysis

The annual enterprise budget for a 210 cow dairy farm calculated for 2015 is shown in the following table with a net annual loss of $370 per head when ownership costs of the dairy farm are included.

The annual enterprise budget for an artisan cheese operation attached to a 210 cow dairy farm calculated for 2015 is shown in the following table with a net annual income based upon 210 cows of $943 per head.

The annual enterprise budget for an anaerobic digestion handling manures from a 210 cow dairy farm and whey from an artisan cheese operation calculated for 2015 is shown in the following table with a net annual income of $10 per head.

Investment costs for adding the artisan cheese operation to the 210 cow dairy farm are shown in the following table. How the cheese is marketed impacts net income as cheese can be sold directly by the artisan cheese maker (either through a retail store or online) at $29/kg compared to $17/kg or $9/kg if sold wholesale or through a distributor, respectively. Net present value (NPV) for the cheese making facility was estimated at $580,739 and internal rate of return (IRR) was 39%.

Investment costs for adding the anaerobic digester are shown in the following table. Total operating cost was $66,238 with NI of $2,105 ($10/head) based on electricity generated and sale of digester biomass, carbon offsets and services for managing digestion of whey, manure and other organic wastes. Total cost for the anaerobic digester was $320,621 (after a 10% investment tax credit) that equates to $1,527 per head. NPV for the digester system was -$65,378 with IRR of -5.2%.

Alternate Uses for Digester Outputs

Alternate Uses for Digester Outputs

For digesting of manure, COD was reduced from 42,400 mg/L to 5,280 mg/L for a reduction in COD of 87.5%.  For digesting of manure and 15% cheese whey COD was reduced from 47,260 mg/L to 3,753 mg/L, reducing the COD by 92.1%.  This higher level of COD removal in the treatment containing whey could be attributed to the addition of more digestible carbohydrates found in the whey leading to increased microbial activity.

Microbial counts before and after anaerobic digestion are shown in the table below. There was a 3-log reduction in total fungi, a 2-log reduction in flagellates and amoebae, and 1.5-log reduction in ciliates. A reduction of these microorganisms is beneficial to reduce potential for disease in plants that may be grown in the material. While there was no quantitative data, it should be noted that odor was greatly reduced after digestion of both treatments with little to no manure odor remaining.  It could best be described as smelling like wet soil.  This reduction in odor would have positive affects if the location of the farm utilizing this material was close to urban areas.

After digestion, the manure shows a substantial decrease in ammoniacal nitrogen and a much higher level of nitrogen from nitrates as shown in the table below.  This decrease in ammoniacal nitrogen directly relates to a decrease in ammonia that would be released into the environment.  Using anaerobic digestion as a method for treating manure would greatly help to diminish ammonia levels at the dairy farm.  Effluent from the combination of manure and whey treatment shows an increase of nitrogen from nitrates of 33% over manure digested alone.  This increase could be attributed to the nitrogen found in the proteins found in whey.  Both effluents exhibited much larger portions of nitrogen from nitrates, phosphorous, and potassium than the potting soil.

Density, total porosity, air capacity and water holding capacity of the digester biomass compared to a potting mix composed of composted bark, sphagnum peat moss, and perlite are shown in the table below.  The water holding capacity of both treatments biomass was significantly higher than that of the potting mix. There was no difference between either treatment in water holding capacity.  Total porosity and air capacity of each treatments biomass was also much higher that the potting mix but not from each other. 

Re-evaluation of Digester Economics

Based on computer modeling of anaerobic digestion it was determined that maximum biomass production could be achieved if the HRT was reduced to 3.3 day. For a 210-cow in which manure is mixed with 25% whey this would produce 3.93 yard³/d of biomass and 12,300 ft³/d of methane.

Net present value (NPV) and internal rate of return (IRR) at 12% discount rate over 20 years was then determined based on the wholesale price of the biomass and the renewable energy credits (REC) for electricity generated as shown in the Table below.

If the REC remains at $0.01/kWh and sale price of biomass is $0.95/ft³ install an anaerobic digester is not economically feasible for a 210-cow dairy and cheese operation It has a negative NPV of $-18,205 and IRR is only 7.64%. It becomes more favorable when the biomass can be sold at $1.45/ft³, which is $0.50 ft³ higher than its value as compost and still $1.00/ft³ lower than if sold at peat moss value, with  NPV of $114,926 and IRR of 34.7%. These numbers further increase in there is an increase in REC value.