Cows make a lot of milk, but they also produce a lot of waste. Unfortunately, disposing of it or treating it like municipal wastewater isn't easy or easily affordable—especially for small farms. Many big facilities have anaerobic digesters, but their challenge is finding faster, more efficient ways to convert all the waste from their herds.
To help with these difficulties, Universal Sanitary Equipment Manufacturing Co. in Tomah, Wis., designs and builds turnkey pump stations, control systems, tanks, pressure vessels and support equipment for farms, industry and municipalities. USEMCO started out in the wastewater business and later moved into the controls and clean water business.
Tank Design Cuts Retention Time
More recently, USEMCO began seeking a way to give smaller farms some of the same wastewater and waste-processing capabilities as their larger counterparts, including using manure to produce methane and electricity. About eight years ago, it developed plans for a small digester system for farms with 500 cows or less and targeted it at farms with just 150 to 200 cows. Rezin estimates there are about 13,000 of these small farms in Wisconsin alone.
"We developed two prototypes, first 100 gallons and then 1,000 gallons, and followed them with a 30,000-gallon version," says Patrick Rezin, PE, USEMCO's president. "We had to find a way to remove solids and keep the system unplugged, and we realized that we had to flush solids away from the bottom of our tanks or skim them from the top. So we came up with a combination of valves, standpipe and vents, which could be opened and closed on the opposite side of the tank, and this system can be automatically monitored and controlled."
In fact, USEMCO already has one of its patent-pending Bi-gester systems up and running at Wayne Peters' Peters Farms Inc. in Chaseburg, Wis., which is one of six founders of the 1,834-member Organic Valley Cooperative. The 30,000-gallon tank was installed two years ago, and takes in about 50 gallons of waste every 15 minutes, or about 7,000 gallons per day from the farm's 200 Holstein cows (Figure 1).
After four or five days, the anaerobic digester begins to produce biogas, mostly methane, which goes to low-pressure storage and a 100-kW generator. It heats water for the digester and preheats water for washing the barn's parlor where the cows live. The generator also heats the parlor in winter, which saves $5,000 per year, and sends electricity back to the local grid (Figure 2). Rezin estimates that Peters' single Bi-gester saves about $30,000 per year in electricity, but it provides several other benefits. "First, heavy solids and liquids from the digester are easier to turn into fertilizer in the farm's lagoon, which saves the owner another $50,000 per year in fertilizer costs," explains Rezin. "Also, light solid fiber from the tank can be run through a screw press to produce excellent bedding for the cows that's almost as good as sand, and this saves another $30,000 per year." In all, the digester system will have a six- to seven-year payback.
Rezin adds that USEMCO's initial one-tank system is scalable and can be expanded to two, four or even six 30,000-gallon tanks for larger farms and herds, or as an existing farm's needs change. "Our tanks are also more portable, and so they're also useful when financing isn't available for a big, in-ground tank," adds Rezin. "Also, one of Bi-gester's most important advantages is that its 4.5-day retention time is much shorter that the 20 days required by other digesters."
Remote Monitoring and Control
Rezin reports that USEMCO's Bi-gester uses two PLCs to control temperature, level and pressure reported by sensors, as well as manage timers and logic settings. However, as more farms put in more tanks, the sensor inputs and PLCs that users and USEMCO must monitor and manage is likely to multiply quickly, and personally visiting all these small, far-flung farms will become impractical.
To solve this challenge, USEMCO is linking the PLCs on its digesters to 2005CD industrial, virtual private network (VPN) routers from eWon, which provide secure, encrypted, remote access via cellular modem or via a local Ethernet connection, as well as monitoring, alerts and alarms, data logging and control. USEMCO and its client also use eWon's Talk2M Free cloud-based infrastructure to connect to the remote routers. Talk2M is also designed to manage and simplify documentation, device management and user authentication, and kick out any unauthorized entities. Enhanced data collection is achieved by several flexible options, such as exporting comma-separated-values (CSV) software files to an application programming interface (API). As a result, 2005CD's remote login capability allows users to monitor, adjust and reprogram Bi-gester's PLCs at a distance, which means USEMCO's technicians don't have to visit each local site to monitor, troubleshoot, maintain and adjust a digester's operations. And, besides only allowing access to predetermined devices, eWon's onsite routers can also be equipped with a physical key switch, so users can turn their VPN on and allow remote access when desired.
"Now, when any of the digester's temperature, level or pressure sensors goes out of whack, the router sends a text message or email to the user's smart phone, tablet or PC and to USEMCO's office as well," says Rezin. "This also means the farmer can control equipment in the tank building and digester and in the control and generator rooms from his laptop and smart phones, and we can do it as needed."
Likewise, eWon's routers are combined with the virtual network computing (VNC) capability of the digester's operator interfaces, and this allows remote users to log into the display and navigate the screens to see how the digester is performing (Figure 3). Collecting data to build a database helps evaluate critical digester operations and determine necessary changes. Digester temperatures, biogas flows, biogas pressures, generator status, power generated, tank levels, water temperatures, pumping totals and room temperatures are just some of the data files being collected.
Next, the routers are programmed to email status updates eight times a day, and send email and text messages if alarm conditions exist. These messages are sent to multiple individuals, depending on the type of alarm. Along with the data-collection and alarm functions, other software polls the digester's electric meters and posts data to the web. This allows the farmer, generator-service technician or other users to view the generator's kilowatt output and other data.
"Our engineer, Mike Harris, wrote the code, so our PLCs could run through eWon's routers, and this gives us the access to tweak parameters and troubleshoot remotely," adds Rezin. "The routers talk to eWon's server, and this allows us to establish a VPN between each digester and our PCs at USEMCO. In the future, we'll be able to monitor the temperature, pressure, flow and other key parameters of all our customers' digesters from our office. We also want to add eWon's routers and remote monitoring capabilities to the 8,000 pump stations we already have installed in the field.
"Where we previously visited a user's site every couple of days, we can now go just couple of times per month. And all those former two-hour roundtrips each become five-minute jobs. We estimate that remote access will save about 80% on our visits, which also means we can grow USEMCO faster because we don't need as much new staff. In the past, where we might need one full-time technician per farm, we can now have one monitor and manage 10 or 20 digesters."