Intelligent residue treatment: converting waste material into high-value products
Waste to many people is the by-products of the production process – such as slurry, manure, waste water and scrap materials. This is what I call output waste.
In pig farms, however, a very significant source of waste is what I like to term as “input waste”
Input waste is very important because it:
- has the highest cost;
- adds no value to the production process;
- is the easiest to control and
- causes additional treatment and disposal costs.
Examples of input waste are:
- Feed spillage. Spillage happens mainly because of poor feeder design or poor feeder management. Feed spillage is a big issue as it is a direct cost and also has a disposal cost. Under Philippine conditions a ten percent feed wastage level per pig will cost a producer 25 kg of feed at a cost of USD 12 to 15 per pig. This means that a standard finishing barn with 1,000 pigs will cost a minimum of USD 12,000 per batch.
- Another source of input waste is low animal performance. These are the wasted opportunities. An example would be a high-performing sow and a low performing sow. We all know that a sow consumes an average 1,200 kg of feed per year and produces 20 piglets per year, i.e. producing one piglet requires 60 kg of sow feed.
If you compare a low-performing sow to a higher-performing sow weaning 30 piglets per year then the more efficient sow only needs 40 kg of feed to produce each piglet. Or, looking at the numbers in a different way, a more efficient sow produces an additional 10 piglets for the same amount of sow feed. This is not a bad situation.
The first step to achieve high sustainability is to reduce your input waste and increase operational efficiency. The less input enters your farm, the less you have to pay for transport, treatment and disposal of it.
The second type of waste are the actual “output waste products”, i.e. the slurry produced by the animals on the farm.
Managing slurry is not easy and has the following challenges if not done correctly:
- air pollution;
- water pollution;
- soil pollution;
- costly water treatment facilities;
- costly sludge disposal costs.
So the general approach to sustainability is to:
- reduce feed wastage and
- to improve animal performance and reduce output waste by
- reducing water usage and
- converting slurry from a waste product to a high-value product such as fertilizer and fuel.
Feed spillage in a barn
The picture above is a classic example of high input waste. Here, you can see feed spillage all over the floor, in contrast to the picture below, which shows minimal waste from a well-designed and well-managed feeder. The high feed spillage situation is not pretty but I see it very often, in some cases on a very massive scale.
A feeder dispenses the feed
Another source of high input waste is the typical solid floor. This means every wash-down floor system that consumes a lot of water as shown in the picture below. If you compare this wash-down system with the alternative pit recharge system
Pit recharge system
that does not require daily washing of the floors, you save a lot of water because the slurry from the pigs will fall on the floor, dry up and then fall through the slats as the animals move around the pen.
Building a pit recharge system
A pit recharge system is built by putting up the pits first and then placing standard 2.4 by 1.2 m cast iron slats over the pits as shown above.
When all the slats are in place, the pre-fabricated building, penning, ventilation and feeding equipment are installed. Finished!
Apart from cleaning, water is also used to enhance animal comfort in many open house farms. Pigs in hot environments are usually sprayed with water as shown below, to improve evaporative cooling and to wash slurry off their skin.
However, newer farms are designed to be cooler and do not require cooling pigs by bathing them. New farms are built with more insulation and they feature completely enclosed, climate-controlled buildings like the gestation barn pictured below.
In Asia, we usually use exhaust fans in a negative pressure evaporative cooling system. The fans, as shown below, pull the air though the evaporative cooling pads, adding humidity to the air and cooling down the incoming air.
Slurry management options
Managing the output waste from the farm basically means converting the slurry from a waste product to a high-value product. Slurry is made up of faeces, urine and water.
In many parts of the world, slurry is called “black gold” because of its capacity to increase soil quality. Slurry has all the 13 essential elements required for plant growth – nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, molybdenum and boron. However, slurry is best applied to the soil after treatment.
In general, there are four ways to treat slurry:
- The direct application of slurry onto the soil. This is not recommended because of the high risk of spreading bacteria as well as the higher cost and inconvenience of transporting a substance with a very high water content.
- The second method is composting, which uses aerobic decomposition by bacteria and fungi to produce a clean, high-nutrient fertilizer.
- Another option is fermentation – this process uses anaerobic bacteria to convert the nitrogen into methane, carbon dioxide and a sludge. This is sometimes called biogas system or collection and use of biogas as shown below.
- The final way is co-composting, which is the combination of the anaerobic and aerobic processes to produce methane gas and a high-nutrient fertilizer. When composting the slurry through aerobic decomposition, this process requires the following conditions:
- availability of sufficient air – oxygen;
- a dry matter (DM) content of 30 to 55 percent;
- a temperature of 60 to 70 °C.
The objectives are to:
- produce a high-quality fertilizer that will increase soil fertility and prolong nutrient availability for plants;
- reduce the volume and weight of the slurry by removing the water portion by evaporation, and to
- sanitize the slurry so it contains no dangerous pathogens.
Advantages of composting
One of the reasons why composting is so effective in supporting plant growth and unique from chemical fertilizers is that compost has humic acids that make the nutrients in the soil easier to absorb for the plants.
Composting reduces the moisture content from a starting level of 77 percent to 30 percent. Sanitation of the slurry is achieved during the main rotting phase where temperatures can reach up to 70 °C, effectively killing the infectious pathogens in the slurry.
Residue treatment with CompoTower
Composting can be done efficiently using Big Dutchman’s CompoTower, which has a daily capacity of 16.5 m3 of poultry manure.
CompoTower has a loading bucket on the left side which is filled by a small loader. The material inside the tank is then mixed with specialized blades that also bring in pumped fresh air to mix with the material. Eventually, the material is discharged from an outlet at the bottom portion.
CompoTower – vertically enclosed high-quality fermenter for slurry
The final product looks like dried coffee grounds. Depending on the DM content of the slurry, the treatment can take between five and 16 days. The drier the material, the shorter the composting period. The final DM content is 20 to 30 percent, with more than 50 percent organic matter and no detectable E.coli and salmonella bacteria.
While power consumption for operation of CompoTower is 396 kWh/day, this is compensated by the income received through the sale of the fertilizer.
Fermentation or biogas system
The next option for slurry treatment is by fermentation or what many call a biogas system.
The benefits of a biogas system are
1. odour reduction and control;
2. improved waste water quality;
3. supply of renewable fuel – this is the main driver for many farm owners in Asia given the high power costs;
4. production of liquid and solid fertilizer products;
5. possible zero discharge of the water when matched with a recirculating recharge system for the pits.
The biogas system can improve the waste water’s biological oxygen demand (BOD) level from 4500 mg/ml to 65 mg/ml.
The final method is the co-composting system, where the slurry is first subjected to fermentation to produce biogas. The resultant digestate and sludge are remixed with fresh slurry to produce a high-quality fertilizer through composting.
In conclusion, my take-away message is: waste not – want not.
You need to reduce the waste from the beginning by improving farm operations and converting waste material into high value products to ensure the long-term viability of farms. There are currently farms in Asia which are doing this. Therefore: if it exists, it can be done.
Managing Director of BD (Big Dutchman) Philippines
The article was published in the LaMB Philippines Magazine - Volume 4 No. 10, 2019. Ty originally presented the above article during the ILDEX Forum Philippines held recently at the Century Park Hotel Manila.