149 lines
5.8 KiB
Plaintext
149 lines
5.8 KiB
Plaintext
These oooplanltton masses are seliaonuolled by eating
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out their algal ioods, and can in their tut-n be eaten by
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rash in Subsequem pond systems.
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01 the pH, which varies troth Inngstum and in
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214mm eyeles, it too increases irom stage to Stage:
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anaerobic pH is 2 .s, taeiilatrve pti 7 5~B 2, and aerobic
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pH 754.5 in clogged algal waters at night, it nray
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climb higher
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At the amblc stage, the BOD ' only 357 mg/l,
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due mainly to nitrogenous compounds, the suspended
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solids 12-50 mg/l inow mainly algae and woplank-
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tonl. About 30% pi these have been removed and
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incorporated into lite iorms, and the metal levels are
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now down to World Health Organisation standards,
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The water can be used tor irrigation, or iiltered via rush
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beds tosiieants
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Seasonal changes are noticeable, in winter, more
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hydrogen sulphide is given oii by anaerobic ponds
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ts-ls mg/l compared with summer-s H rag/ll, and
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wtnds rrtay rontribute more to oxygen levels in open
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ponds than do algae, tn winter too, more ammonia
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tell-id is released to the atmosphere.
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Summer sees residues oxidised to nitrates The
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oxygen being provided more try algae than by wind,
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less hydrogen sulphide is given oil, and there are
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greater ranges at temperature in winter (lo—IS'CD,
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decornposrtton slows and sludge levels build up, only
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to be more actively converted in the summer warmth oi
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ILZZT (“JPN BO D is 495 ltg/ha/day in winter,
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mat lrg/tia/day in summer tat optimum pond
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eonditionst, showing that activity almost doubles as
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temperature increases Consequently, almost twrre as
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much gas as methane is given oii in summer tor in
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irrrrrrd drgesterst in winter. the cooling water ot
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methane—powered engines can provide the essc '
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heat to drgesters via a closed loop pipe
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in all, this simpte lagoon series produees a very
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beneticral eiiluent irom heavxlyspullmed iniluent
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However. there are even more sophisticated biologrral
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treatments is Hedithuse eiteeted lay the higher
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plants As on tried below, some genera ot rushes,
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sedges, and iloaiing plants ran greatly assist with
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removal oi heavy metals and human pathogens. but
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perhaps more imponantly, some plans can also brealt
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dawn halogenated tehlorrne, bronunel hydrocarbons
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synthesised as herbicides and pesticides
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lsrael (Ntw Scientist, 12 Feb 7‘?) leads sewage waters
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to long eanalised ponds, aglmed try slnwlysrlvulving
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paddleswheel aerators ponds are 0.5 in or less deep
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Under bright sunlight ior under glasshouse eoverst
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dense algal mats ior-rn. and these are broken up by the
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addition oi alunuiuum sulphate ta pollutanllt, slrimmed
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our drained, tentrihrged. steam—dried, and ted ma'mu
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carp or ehieltens ialthough l imagine that arp could
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sellst'eed on aguatre algaet Algal protein replaces soil
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oi soya bean protein in teed rations to poultry Total
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treatment by these methods takes about 4 days The
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water is alkaline and somewhat anaerobie, needing
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more agitation in winter or on :00! days. Holland runs
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sewage to srrrular canals, and reaps reeds m plants as
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green erop or tor erait supplies.
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it has been iound (Ems u. winter '85! that the
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arriiicial aeration oi iamrlative ponds is most eiiietent ll
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run at intervals at two hours in s lanai, oi the nmet
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The taeulattve bacteria lollow Iwo digestive modes. and
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operate best ii a rush oi r is supplied aiter a itmr-hour
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anaerobic period, excilelillg earbon dioxide and thus
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reducing the bullt oi sludge There are corresponding
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reductions in energy costs ior aeration. Nitrogen was
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reduced iroin 20 mg/l to less than 5 mg/l, phosphorus
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irom s 5 mg/l to less than i mg/l when terrie chloride
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was supplied, The process has been dubbed A.A.A
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iattemairng aerobic and anaerobiet digestion
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nius, agitation oi anaerobic systems by bubbling with
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«impressed methane, and A A A oi iaeulatrve ponds
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can be used to obtain useiul yields oi methane and
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hishrpmleln alage irom sewage As tor the aerobic
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ponds, such higher plants as water hyaeirtth removed
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res dual metals, surplus nutrients, and ttecsir group oi
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b i (Nero Selentrsr, 4 0d ‘79, p 29t Microwave
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radiation can also be eiiective at breaking up algal mats,
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and sterilising algal pmducls, eliminating toxre
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alumimum salta
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As ior temperatures, solar ponds used in eonntrwtron
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with compact anaerobic ponds can supply the low
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grade heat necessary tor eiitoent sludge digestion. and
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methane will drive any motors needed ior both aera.
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oon and the gas compression used tor the agitation oi
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sludge, The whole processing system can be made very
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cumpacl, and at the aerolare pond level, throughitow
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ean lae led to tirewaod or tuel iorost systems, to
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irrigated grasslands tas at Werribeel, or via trieltls
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irngatron in mops in and areas.
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rioal treatment, now in use in Holland and
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recommended by scientists at the Mar Planelt lnstthite
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in Switrerland, can be released via a sinuous, sealed
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eanal ot a variety oi mshes and iloaiing water plants,
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Waters polluted with metals, bioodes, or sewage can
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be cleaned by travelling through raed beds oi Strrpvs,
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Typira. arid lunevs, or by harvesting oii iloaiing plants
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such as water hyaernth The nrsties and sedges can be
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mown and removed periodioally tor mukh oreellitlose
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Fm untreated sewage, a holding time ni “Lu days is
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neeessary, or travel through a serrcs oi mzzplike
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gravel rlter tanalr with iloaiing weeds and sedges ror
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swimmrng pools and less polluted systems, a pumped
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'sytle- oi water through terns, rushes, and watereress
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suiiices to remove urine and leaves Such pools need a
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23.30 em (9-!2 rneht eoarse river gravel base, with
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intalte pipes below, and a skimming notch ior leaves
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apestes recommended are
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- phrrgrnrtes eorrrnrvrrrs and spp., Typhr spp-
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Florculate colloids, dry out sludges, eliminate
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pathogens
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- SChaawptnilu spp, Takes up copper. cobalt, mrlret
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manganese, exudes mould antibiotics.
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- 5rrrpvs sppi breaks down phenols, ineludmg toaie
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pentaehloiophenol
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Low to zero populations oi : soil, eohiorm barmt-ia,
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Salmonella, and criteroeorei are lound atter water is
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177
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