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  • Richard

CWIS and Japan

A colleague sent me a link to the ADBI Johkasou video. When I visited the Osaka Sewerage Museum a while back, and also saw the impressive wastewater treatment plant outside, I had understood that the 'cess pit'/vault toilet approach to urban household sanitation was being replaced by sewerage for all. So interesting to learn more about the Johkasou 'enhanced septic tanks' being deployed since 1987.

Particularly as England passed a regulation last year (without communicating this to anybody directly, typical!) that we now have to have similarly enhanced septic tanks such that my only partially enhanced shared septic tank perhaps needs some attention?

Back to Japan, noting that the video talks about these units being used for rural and suburban areas (it would be interesting to know the extent of the sewerage in this context and where the Japanese ‘urban/suburban’ boundary lies), taking the figures quoted in the video and the information from the 2006 Gaulke paper it would seem that the enhanced septic tanks cost $7,500 each (updated to 2020 prices), hence the subsidy per tank is $3,000.

And, with some heroic assumptions about household sizes over the period, that the average annual subsidy (in 2020 prices) has been $254 million ($1,260 per person), $8.4bn over the 33 years (or $335m per year over the past 20 years), in order to serve approximately 6.65m people (at time of construction) - Gaulke’s figure of 8m served in 2000 not quite agreeing with the other figures.

The costs tie in with costs currently being quoted here for 'household wastewater treatment plants' but, as the colleague pointed out, Japan funds an annual inspection for water quality with presumably the household funding the annual desludging and 'a few times a year' required maintenance by the 200,000 trained and examination qualified registered technicians. What we called 'indirect costs' in WASHCost and it would take even more heroic assumptions to estimate that cost. Also, something that the new system in England has definitely not funded!

Gaulke (2006) On-site wastewater treatment and reuses in Japan, Proceedings of the Institution of Civil Engineers, Water Management 159, June 2006

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