- Decem~er 1977 RAIN Page 5 WASTING WATER treatment needs below the thresh~ld where expensive contractor-installed septic and drainfield or sewer systems are necessary to where simple owner-installed and -maintained treatment· systems are adequate. Such systems may cost $50-$100 or lessonly 5 to 10 percent of the cost of a septic/leach system, and only one percent of what a sewer installation would cost. Simple on-site greywater treatment is necessary to realize the full benefits that dry toilets present as an alternative to central sewage treatment. Together, they possess the following advantages: _· ' • On-site systems can cost only a fracti.on of central systems and lessen the massive financial burden central systems place on individuals and ,communities. • They avoid the land "development" push resulting from central sewer installations. • Water is typically returned to the local water table by dispersed release of the wastewaters in small doses. • . • No final effluent disposal problem is created as with the large plant. • The estimated ·cost benefit with dry toilets is that of a water economy of 45 percent, or 4,000 to 6,000 gallons per person/ year: • With the water economy of dry toilets, a lot of land and therefore many building sites would become available where eitber·water is in too short supply for conventional use of flush toilets or wastewater is difficult to dispose of because the size of the lot or soil characteristics prevent adequate drainfield installation. • The proper maintenance and repair of on-site systems upgrade~, rather than abandons, an investment in on-site sewage systems already ~ade by pre-existing housing- estimated as 16-20 million homes at $1,000, or 16-20 billion dollars in the U.S.. The disadvantages of such on-site treatment systems are less concrete, and more a question of lack of experience with them or adequate standards for their use: • • Management systems for decentralized on-site installations are not well developed. • On-site systems commonly leave so much to the discretion of the operator, especially for the ultimate waste and wastewater disposal, ,that regulatory agencies _view control as difficult if not impossible. • The legal basis for right of entry on private property for regulatory inspection of these systems has not been clearly established. • • The actual standards for construction of on-site systems va~y enormously, have a poor record for compliance, and have so often contributed to their failure record that on-site systems are accepted with difficulty by regulatory agencies, and have been bypassed in favor of replacement by central treatment plants (although the actual performance record of central treatment plants is much worse than assumed by those same regulatory agencies). • Although the presence of disease agents in human waste has been well documented, the health risk associated with on-site systems has had no modern-day evaluation. Treatment necessary for greywater depends on volume, degree of pollution of the water, and intended reuse. The main treatment problems are: • Breaking down food wastes without offensive odors or attracting flies, rats, or other creatures that may cause nuisance or health problems. • Soil clogging that prevents necessary absorption of water into the ground.. • Care and maintenance of the treatment facilities to ensure continued effective operation. • Additionally, where human contact in reuse of the greywater is involved, or where discharge of the greywater may affect the health of others via contamination of groundwater, streams or rivers, the reduction of possible human disease organisms to safe levels is necessary. Separate; treatment of toilet wastes and-greywater and demand for surface reuse of greywater is relatively new and· almost no health standards have been set for discharge of greywater. Actual health hazards are extremely difficult to determine, and the main difficulty of setting standards for greywater is to avoid arbitrary and unrealistic standards. Rural and single-family use of separate greywater treatment probably should require less stringent control than urban use, as they are to large degree self-quarantined by ·geography ·and present much lower health hazards. Water quality statistics usually make a point of the higher pollution level per volume where dry toilets and other water conservation measures have been taken, while ignoring that there may be a lower TOTAL of pollutants released from the house. There may be a valid case also for allowing higher concentrations of pollutants in wastewater from low-discharge households than in larger wasteflows, as the total pollutants are much less and more likely to be within what the soil, air, and plants can absorb, transform and make use of without harm or further treatment. The OAT report contains an excellent overview of greywater chemical and biological quality and details for treatment and reuse of greywater. Get a copy if you plan to install a separate greywater system. - TB
RkJQdWJsaXNoZXIy NTc4NTAz