Environmental Wastewater Treatment Systems provides engineering, manufacture and installation for advanced, environmentally improved wastewater treatment systems using the Stahlermatic technology developed in Germany.


    The Society of Professional Engineers of Puerto Rico (CIAPR) gave the "Outstanding Engineering Project of 1994" to a Wastewater Treatment Plant using the Stahlermatic Design. This was the first time in the history of the award that a wastewater treatment plant had been so honored. The plant has been operated by the Palmas del Mar Utility Corporation, Palmas del Mar Resort in Humacao, Puerto Rico, for the past ten years.

    The same installation technology was given EPA's Region II Award in 2004 for Outstanding Technology combining water treatment and composting


    Usually wastewater treatment plants are designed to comply to discharge standards and treat the product as waste. The concept of wastewater treatment plants becoming instruments capable of producing goods with economic value instead of waste while at the same time providing the appropriate treatment is creating a new approach in the wastewater industry in Puerto Rico and elsewhere.


    All treatment plants generate solids. The reality is that a treatment plant is a great solid waste concentrator machine. The more solids that we concentrate and dispose of, the better the water effluent. This system uses the yardwastes (palm fronds, coconuts shells, grass clippings, & shredded tree branches) in combination with the generated stabilized bio-solids in an open windrow compost process to convert the same into soil conditioners.

    The windrow compost process is very simple, but effective, and occurs in drying beds with very simple machinery, instead of using systems for forced aeration and a sophisticated covered building.

    The 200 cubic meters of material processed per month save $60,000/year in yardwaste and dry sludge disposal expenses. Savings in fertilizer purchases are in addition and are still     being compiled. The composting follows procedures of the US Clean Water Act - CFR 40 Section 503 where windrows are turned at least five (5) times in a fifteen (15) day period using a one (1) acre area for mixing and yardwaste processing and another acre for curing. The curing takes 12 weeks; it is stored for landscape applications in projects at the resort.


    Conventional treatment plants are great energy consumers. One of the greatest operational expenses is energy.

    The Palmas del Mar system has been using with excellent results the Stahlermatic submerged biological rotors that allow energy efficiency in the biological stages. This treatment plant has been processing with a constant efficiency of 0.20 kWh for each Kg of BOD5 reduced. If the treatment plant operates at peak capacity, this ratio will diminish to 0.05 kWh per Kg of BOD5 reduced. In comparison, conventional activated sludge processes need at least 1.5 kWh per Kg of BOD5 reduced.


    The Stahlermatic rotors combine activated sludge and fix film processes in the same tank, This combination of processes permits the volumetric load to attain the range of 1.4 to 2.0 kg BOD5 for every cubic meter inside the reactor. In comparison, the more common activated sludge process used in the industry today uses 30 to 60 kg BOD5 per cubic meter.

    Thus, the Stahlermatic combination of systems produces efficiency increases of 273%. The means to achieve such high treatment efficiency at low energy demands is by using submerged rotor aerators (SRA).

    The Palmas del Mar treatment plant uses nine (9) such rotors of four (4) meters diameter that are 3/4 submerged. The 2.5 meter wide cylinder consists of pipes connected to a metal frame wheel joined together by the pipes and the axis. The axis never needs to be lubricated since it always remains submerged. The pipes have slots that capture oxygen from the atmosphere that escapes at the bottom of the tank due to the pressure created by the water depth. The wheel is moved by a small, direct-drive electric motor with a low gear transmission and a 3.5 kWh connected load. Transfer from motor to rotor is by a metal chain surrounding the outside edge of the wheel which provides an excellent leverage and low torque demand. Fix film surface area is created on propylene plastic media located inside the periphery pipes. The (9) wheels produce 1.78 acres of fix film area.


    Using smaller biological reactors saves valuable space. This translates into lower construction and infrastructure costs. So far, for example, the Papas del Mar project has required an investment of $3.6 M for a treatment capacity of 1.4 MGD (millions of gallons/day). The $2.57/gallon of treated water infrastructure cost is one of the lowest on the market today.

    The rectangular basins are supported on piles planned in a modular set-up. Every time an expansion is required only three (3) walls are built. This applies for both the biological reactors and the secondary clarifiers. The ten (10) year old plant has so far received one 0.80 MGD expansion.


    Water is becoming a high-priced commodity. To discharge the same water after all the expenditures to comply with the receiving natural system and not reuse it is simply a waste of energy, manpower, and lack of understanding of sustainable systems. At the Palmas del Mar Plant, the water is reused and discharged into a polishing tank which recharges a pond to irrigate the 18-hole golf course and other landscaping projects that have been developed in this tourist and residential community resort of 6,000 people.

    This water maintains the complex eco-ponds at their designed levels. This provides protection from salt water intrusion from the nearby Caribbean Sea. Water is then returned via the hydrological cycle through infiltration and evapotranspiration. The natural system accomplishes a more advanced treatment than a mechanical secondary system found at conventional wastewater treatment plants. Environmental Wastewater Treatment Systems believes that this integration of natural and mechanical processes will become the trend during the next century.  



    Mr. Peter Grell was born in Hamburg, Germany in 1931. After studying Mechanical Engineering in post-war Germany and later Business Management at New York University, he has pursued a dedicated and illustrious career in the hotel industry serving in various engineering capacities at such hotels as the Stanhope in New York, the Baton Rouge Hilton (Louisiana), and most recently the Condado Trio in San Juan, Puerto Rico. For 10 years he was Vice President of Palmas del Mar, in charge of Engineering, Condominium Management, Communications and Energy. Mr. Grell is a Member of the Caribbean Hotel Association. Since 1992, he has represented the Stahlermatic technology in the Caribbean.




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