From: Oz <Oz@upthorpe.demon.co.uk>
Newsgroups: sci.bio.food-science,sci.bio.microbiology
Subject: Re: IFST condemns UK Government's reported rejection of E.coli safety 
	recommendations
Date: Tue, 25 Mar 1997 09:12:39 +0000

In article <VA.00000074.012714a8@wrcs.u-net.com>, William R Hite
<wrhite@cix.compulink.co.uk> writes

>We do not need to go to Africa to use human sewage for agricultural
>purposes - the UK uses quite enough. I have no objection to its use as
>such - merely the slurry^H^H on parts foreign :-)
>
>Of course sewage sludge is not the same as raw human sewage, but clearly, from
>the
>restrictions on its use it cannot be entirely free of nasty things. Further, the
>regulations do also state that untreated raw human sewage may be used.
>
>How well is all this policed?

Hmmm, well I use about 2,000,000 gallons a year.
Rigorously.


>Sewage Sludge
>-------------
>        These regulations say, inter alia, and as best as I could note
>        them from a conversation with an EA official:
>            -there are limits on heavy metal concentrations in the
>            soil

Correct, although this is not a problem these days as contaminated
sewage costs (the producer) so much they decontaminate before discharge
to the sewer. In fact given the low trace element status of my farm, I
wish the levels in sludge were higher. Particularly copper and zinc,
although I could do without the lead, chromium and cadmium. Regular soil
tests ensure the maximum levels are not exceeded. Currently I am good
for the next few hundred years unless sludge levels change.

>            -no livestock to graze on such land for 3 weeks after
>             application

Correct. This is exceeded, usually by several weeks.

>            -no fruit or vegetables normally eaten raw or grown in
>             direct contact with the soil shall be harvested within 10
>             months of application

The somewhat variable quality would (except for 'organic' produce) make
it far from ideal for vegetable growers to use. The crop losses alone
due to it's variable fertiliser content would be horrendously expensive
in a conventional system.

>         They further state that:
>            -untreated sludge, i.e. raw human waste, can only be used
>             if injected into the soil or, if spread on the surface,
>             must be worked into the soil as soon as practicable
>            -once worked in the same limits as for treated
>             sludge, above, apply

Dunno, never use untreated, never will, wouldn't want to.
It's not available locally anyway.

Agronomically the use of sewage sludge is very difficult. The product is
highly variable (even from load to load) and the traffic that is
required causes damage (sometimes severe) to the soil, although
irrigation is possible it's use is not popular with the operatives. (!)

The variability means that it's use is significantly restricted since
the level of nitrogen used on crops, and the timing, is typically highly
critical. For organic produce that rarely has anywhere near the optimum
nitrogen applied it could presumably be used all year. Winter
(irrigated) and summer use on grassland is ideal since grass has a
nitrogen response that typically is straight line up to close to
1000kgN/Ha but applications rarely exceed 500kgN/Ha and so the nitrogen
is useful, and the phosphate (from phosphatic water softeners) is
appreciated. The most effective use is on grass for conservation where
the 3 week grazing restriction is easily significantly exceeded. For
cropping the only really useful crop is oilseed rape, that does not
respond as badly as most crops to exceeding the optimal N rate and where
the timing of the N is rather uncritical. A reduced (say half) rate
application in summer which is then ploughed in is quite useful for
winter rape. Spring oilseed rape is a minority crop (the yields are very
low) but the window for application is very wide, probably from
September to March, and the low yield means that missapplication has
limited effect (you lose money either way).

The water board I use (Thames) get highly agitated at the merest hint of
a thought that the regulations are not explicitly followed and
preferably exceeded and one has to sign an agreement stating that you
will obey the regulations. They do check up and will refuse to supply in
future if they are not followed, indeed I wouldn't be surprised if they
prosecuted.

Note that treated waste is the sludge formed by standing the treated
waste in large tanks. The supernatant liquid is returned to the
watercourse and complies with the very strict regulations that this
requires. I doubt that the sludge is a hazard even when it is fresh and
before it has had a week standing in the works and three+ weeks exposed
to the sunlight.

I don't think you can compare a well regulated and monitored plant in
the first world where spares and expertise are permanently on line with
a third world 'plant' in a country where (probably not through any fault
of theirs) repairs and many spares take quite a while to deal with.

Also note that (see promed) pathogens in UNtreated sewage are in fact
very low. The figures that were given there were a few pathogenic
bacteria per liter, indeed so low as to be difficult to measure. I find
this surprising, but still. Whether this is also the case in the third
world I do not know.

--
'Oz     "Is it better to seem ignorant and learn,
         - or seem wise and stay ignorant?"