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The above assessments of population (P) should be used for both existing and new properties,

Larger luxurious houses tend to have greater loads and increased water consumption with variability.

Holiday homes tend to have higher occupancies with perhaps lounges also acting as bedrooms. Holiday lets and second homes may be used intermittently

Check for unusual water uses such as spa baths, home brewing or home photo processing.

Waste disposal units increase biological load.

Laundry chemicals and toxic substances will affect the performance. (See below) It is assumed that laundry is not brought in, i.e. Team strips.

  • Water saving devices affect sewage strength, the impact of their installation should be identified.

  • Laundries affect sewage strength and treatability; their proportion should be identified.

  • Surface/storm water is not permitted as part of the wastewater stream and must be excluded.

  • It is assumed, unless stated, that waste disposal units (WDU) are not in use.

  • Undersizing of equipment is to be avoided as it is always better to have a plant slightly oversized, rather than on the limit or undersized.

  • The owner of the equipment holds the consent to discharge and should be aware that he is responsible for the effluent quality discharged. Thus all sources of discharge into the equipment must be declared.

  • After installation, if the equipment is overloaded, due to activities that were not previously identified by the owner/ purchaser of the equipment, then the manufacturer may not be able to assist with meeting the legal obligations of the consent provided by the regulator. Consents may change at intervals. The regulator has the right to review consents at regular intervals.

  • All sewage treatment equipment should be maintained according to the manufacturer’s instructions by a certified engineer trained in accordance with the British Water Maintenance and Service Code of Practice (in preparation).

6 C o m m e r c i a l P r e m i s e s Identify ALL the sources of waste. Identify final maximum site usage/business expectations. The individual values provided for each function within the table assume that 100% of every application and load is quantified. DO NOT reduce values based on reduced expectations.

  • All catering applications require the installation of adequately sized grease separators, removal or retention systems up- stream of the biological treatment equipment.

5 D o m e s t i c H o u s i n g A treatment system for a house with up to and including 3 bedrooms shall be designed for a minimum of 5 P.

  • The size of a treatment system for a house with more than 3 bedrooms shall be designed by adding 1 P for each additional bedroom to the minimum single house value of 5 , eg:

7 C a t e r i n g p r e m i s e s Establish maximum (and minimum) daily load based on a 24 hour cycle.

  • Check period of operation.

  • Identify dates of maximum loads, e.g. Mothering Sunday,

Easter, Bank holidays, Fridays etc.

  • Identify load peaks, usually at lunch or evening.

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      house with 3 bedrooms = minimum 5 P system

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      house with 4 bedrooms = minimum 6 P system (5+1)

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      house with 6 bedrooms = minimum 8 P system (5+3).

  • A treatment system serving a group of houses shall be designed by adding together the P values for each house calculated independently, eg:

    • -

      for a group of three houses (3, 4 and 6 bedrooms respectively) the system shall be for a minimum of 19 P (5+6+8)

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      an estate of thirty 4-bedroomed houses will need a treatment system for a minimum of 180 P (30 x 6).

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      Where there are larger groups of houses, the P should be estimated using both the expected total load and the flow, considering both peak and total flow

  • These are minimum recommended population (P) loads, they should not be modified downwards: upward modification may be necessary because of particular characteristics of each property or groups of properties.

Flow balancing may provide an appropriate solution.

Where WDU and potato peelers are to be used calculate/document the load.

Identify the nature(s) of the catering in order to select the correct loading, eg

Bar snacks

- ploughmans, sandwiches, basket meals, etc.

Pre-prepared catering

- frozen and chilled meals (not prepared on site).

Home cooked meals

- fresh soups, fresh vegetables, casseroles, etc.

Luxury catering

- fully prepared on site with cream sauces, home made desserts.

Takeaways Fast food

- Indian, Chinese, fish and chips, etc. - roadside restaurants, burger chains, etc.

  • For groups of small 1 and 2 bedroom flats , a total P load shall be calculated specifically for each group and consider the maximum possible occupancy and flow.

Function room catering - Establish “normal” style, may be sandwiches, or full buffet, home cooked meals, conference, wedding banquets, etc.


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