Treatment of lower load graywater by using a controlled soil natural treatment system.

Experiences of treating graywater by soil natural treatment systems have not been widely reported. In general terms, graywater has a lower concentrations of organic matter; nutrients (e.g. nitrogen), and microorganisms than combined wastewater; therefore, the graywater treatment capacity of soil should be evaluated. In this study, the performance of a natural soil treatment system was evaluated when shower graywater from a house located at Sapporo City, Japan, was treated by a layer of 30 cm of soil from the Hokkaido University Campus. Results showed very high removal efficiencies of chemical oxygen demand (98%) and Kjeldahl nitrogen (95%) at high infiltration rates (214 cm/d), which denotes that natural soil treatment systems could be a good alternative to treat lower load graywater.

Design and operation of the bio-toilet system.

Criteria for the proper design and operation of the bio-toilet have not been established either by the manufacturers or by the authorities. Based on the results of experimental research already reported by us, criteria for the proper design and operation of the bio-toilet system were established. The establishment of operation criteria led to the formulation of an operation scheme where three main zones are distinguished: i) green zone, where the best composting performance is expected; ii) yellow zone, where biodegradation can be conducted but performance is not the most efficient; iii) other zones where operation of the bio-toilet is not recommended because odour problems and human health risks will develop, or in the worst case, biodegradation of faeces will not occur. In the design criteria, the surface area required for evaporating the water loads due to contributions of urine and faeces was determined by applying concepts of drying theory. This theory was also applied to estimate the mass and volume of dried sawdust required for dealing with the critical water loading. However, the accumulation of stabilised solids transpired to be more critical and, finally, mass and volume of dried sawdust were estimated based on this factor.

Onsite wastewater differential treatment system: modeling approach.

In this paper, the Onsite Wastewater Differential Treatment System (OWDTS), a new approach for improving the traditional onsite wastewater treatment systems (OWTS), is proposed based on differential management and treatment of household wastewater effluents. Three fractions of household wastewater have been differentiated, reduced-volume blackwater, higher-load graywater and lower-load graywater. Based on this differentiation, different treatment processes required for each fraction are discussed. The procedure adopted for treatment of toilet wastes (reduced-volume blackwater) is shown. In the case of graywater, a sketch of treatment processes is provided. The OWDTS seems to be a new approach with higher potential for improvement of traditional OWTS, dry ecological sanitation, recycling of resources (toilet wastes and water), conservation of water resources, etc. Aerobic biodegradation of toilet wastes by using sawdust as a matrix is an essential treatment process of the OWDTS. Membrane technology seems to be the most effective process to treat higher-load gray water. Natural biodegradation of lower-load gray water by soil bacteria needs to be deeply studied.