Biologic Drainage at Howle Hill Eco-House: Mana System

The "Mana - Biologic Drainage System" project, located in Howle Hill, Herefordshire, focuses on an innovative, ecological approach to wastewater management for a self-built eco-house. This system, designed by Taste of Self Sufficiency and implemented by Biologic Design, aims to eliminate traditional sewage and greywater treatment methods by integrating a Wetland Ecosystem Treatment (WET) System.

The core principle of the Mana project's drainage strategy is to avoid conventional flush toilets and septic tanks. Instead, all liquid toilet waste is repurposed as fertilizer for garden plants, while solid waste undergoes a 12-month composting process before being used as mulch around fruit trees. This approach ensures that no human waste is discharged into a conventional sewage system.

For greywater, originating from sinks, showers, and washing machines, which is estimated to be around 60 liters per day, the project utilizes a WET System. This system is described as a tree-based ecosystem that leverages the natural processes of planted trees to purify wastewater. Specifically, coppiced willows are employed, which can be harvested annually to yield basketry wands, simultaneously removing nutrients from the system. The root zones of these trees are crucial, as photosynthesis byproducts like simple sugars and oxygen create an ideal environment for aerobic microbes, particularly fungi. This microbial activity facilitates nutrient and gaseous exchange over a large surface area, contributing to the purification process.

An additional benefit of this design is the integration of food crops within the swales, which are intended to protect the system from drought. This multi-functional design aims to create a low-maintenance, self-watering, and self-feeding system, effectively eliminating waste and generating multiple yields.

Before entering the WET System, greywater from the kitchen sink undergoes a preliminary treatment to remove solids and oils using a commercial grease trap. This step is essential to prevent clogging and maintain the efficiency of the biological treatment process.

Biologic Design, the contractor for this project, has extensive experience with WET Systems, having developed them since 1993, including large-scale industrial applications. The WET System for the Mana eco-house is characterized as a horizontal plug-flow, multi-species, soil biome-based constructed wetland, incorporating wet woodland and orchards.

A critical aspect of the Mana WET System's construction is the use of an impermeable geosynthetic bentonite clay liner. This liner is necessary because the subsoil is permeable, and it prevents any untreated wastewater from seeping into the surrounding groundwater. Unlike mechanical wastewater treatment systems or even traditional reedbed systems, the WET System integrates wastewater purification with the production of biomass resources and enhances biodiversity by creating a rich, diverse wetland habitat.

From a permaculture perspective, the Mana project exemplifies several key principles: minimal water consumption due to the waterless toilet and greywater reuse, zero waste, and multiple yields. The system provides water treatment, creates a self-watering garden, supports food production, and contributes to soil fertility through the treated wastewater and humanure. This holistic approach underscores the project's commitment to sustainable living and resource management.