Treatment of dairy farms wastewater using a natural biological system
Wastewater from dairy farms is known in Israel and abroad as a polluting factor that requires special treatment. For this purpose, a reform plan was drawn to act as leverage for adapting this field to the contemporary environmental requirements. The State allocates large sums, and many dairy farms underwent this adaptation with the government's support. The reform plan is ending soon and many dairy farms are not even close to a solution.
The Ministry of Environmental Protection funded a number of pilot systems that were meant to provide a solution to dairy farms’ wastewater. None of these pilot programs were found to be entirely successful. This may be the cause for the change in the Ministry policy; now the goal is not to find solutions for wastewater but to minimize the flow by building barriers and other means to completely separate the dairy farm water from environmental sources such as falling rain and runoff. There is no doubt that the barriers prevent a flow of polluted rainwater, however, this does not solve the problem entirely. Many small dairy farms will not be able to afford the costs of barriers, and will be forced to shut down, despite the significant support of the State. Furthermore, the barriers solve the problem of the outdoor area, but not the wastewater of the milking station, which also exceeds the limits on inclusion to the sewage system.
The cows spend around 10% of their time in the milking area and, naturally, their excretions are there as well. Even in a dry milking interface (without rinsing the udders), a lot of water is used in the milking area to keep it clean. This water usually flows to a regional wastewater purification center.
Until recently, the working assumption of the planners and of the Ministry of Environmental Protection was that a simple static divider at the exit from the milking area is sufficient to reduce the level of biological oxygen demand (BOD) to 500 mg/L that are permitted to flow to the wastewater purifying station. Measurements we conducted in 30 milking farms contradict this assumption completely. The actual outlet values are between 1,000-7,000, with an average of 4,000 mg/L. In addition, the BOD is not the only important parameter in the wastewater from dairy farms. One of the other most important parameters is boron.
There is still disagreement regarding the source of the high level of boron at dairy farms. The use of detergents alone does not explain it. Apparently, the cows eat food from boron enriched lands receiving fertilizers and/or desalinated and treated wastewater, and the pollution is concentrated further through their digestion system by the process of bioaccumulation.
The variance of the boron levels measured in the wastewater of milking facilities is high, within the same farm and compared to other farms. The values vary from 1.5 to 10 (!!) mg/L, whereas optimal values in irrigation water are 0.4 mg/L. Boron concentration >3 mg/L is actually phytotoxic to many species. Naturally, a small wastewater purifying facility that receives wastewater from a number of farms, will be highly affected by these values, to the point that the water it produces sometimes cannot be used, even if the water meets the other standards. Boron has a strong effect on the fertility of the land, and irrigation with even a slightly high level of Boron (1 mg/L) will cause direct damage to soil and many crops. Regular irrigation with such water may turn the land barren completely.
Around the world, a variety of constructed wetland methods are used to purify wastewater from dairy farms (and other animal farms), but in most cases they are used as the upgrading stage and not the primary treatment system. The treatment facility that Ofra Aqua Plants built for the Shmueli dairy farm in rural Galilee (Zippori) is unusual in the fact that it received its wastewater following a slight static division and with higher than average pollution loads.
The Shmueli farm is a well-kept and beautiful "reform dairy farm” with 130 milked cows. The natural wastewater treatment facility built by Ofra in early 2000’s was executed in two stages. After completion of the first stage, the owners were not required to further treat the wastewater onsite, according to the above mentioned regulations, and approval was given to have the wastewater flow to the regional wastewater purifying facility. Ofra further decided to convert the facility into a larger pilot, in order to examine the actual qualities and to see how the water purifying system it developed affects these qualities.
Two sedimentation pools integrating plants were planned of an overall size of 100 sqm and three sub-soil pools, streaming high quality water in waterfalls and open ponds for irrigation of olive and grape orchards. The entire complex is destined to become a center for ecological tourism.
After two years of operating without malfunctions, we can say with confidence that the system achieved its goals, and more. The actual results are completely aligned with the plan in all the parameters tested: biological oxygen demand, suspended solids, nitrogen, phosphorus, boron and chloride. The average reduction of the biological oxygen demand in the second year was 97%, solids were removed by 96%, and boron was reduced by 80%. The process with boron is a bit different than the other variables, since the system has to reach a level of maturity (5-6 months) for the reduction process to begin, which may be explained by boron’s neutral electrical charge compared to other minerals which are often found as ions. There is also an impressive reduction in nutrients: 70 % on average of total nitrogen and soluble phosphates.
One of the important traits that characterizes the natural biological system is absorbing severe fluctuation and extreme one-time pollution events without collapsing and polluting the environment. The system faced an unexpected test, when a container of diesel fuel was accidentally spilled into the sedimentation pit by a work accident. Almost every other system would have been severely affected if not destroyed for a long time.
Since the incident already occurred, we decided to take it as a chance to learn, not to do anything, but observe and monitor.
We noticed several noteworthy phenomena:
1. The system was severely damaged aesthetically. Many leaves were scorched and the distress was clear.
2. All the plants survived the severe incident and recovered at different paces.
3. At the exit from the system there were no fuel remains.
4. It was possible to observe the contamination progress through the system and its attenuation, based on the reaction of the plants.
5. 4 months after the incident, there were no signs it ever happened.
6. Throughout the entire period, there was no decline in the performance of the system in all the parameters examined.
According to the frequent monitoring data, we determined that the system succeeded in the difficult yet vital task of purifying the wastewater of the milking farm. The natural biological systems method has been proven to be reliable and as one that can overcome harsh and changing conditions, providing water at the expected level of quality.
Since then, a variety of other livestock projects were designed and executed by Ofra Aqua, including a piggery waste treatment facility in China, in Europe and other dairy farms (including sludge treatment) in Israel, all with outstanding results.