• Liquid waste

    To them it's just a crap,
    to us it's bread and butter.

    Spike Milligan

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Non hazardous biodegradable waste is treated in anaerobic decomposition to biogas (operation R3/R1). 30 tons can be treated daily. The liquid waste passes through a sieve and a crusher before entering the hygienisation tank were heaters heat the liquid waste at seventy degrees Celsius for one hour before entering into the digesters. After hygienisation the liquid waste enter one anaerobic digester of total volume 1,800 cubic metres.

The anaerobic decomposition of the primary and secondary sludge takes place in the three digesters. In one of the digesters, anaerobic decomposition of the hygienised liquid waste takes place. The total volume of the digesters is seven thousand two hundred cubic metres.

Over a period of thirty days, at a temperature of approximately thirty-nine degrees Celsius, anaerobic conversion of the organic matter to biogas takes place. The first stage involves acid hydrolysis, where organic matter decomposes into short-chain fatty acids. The methanogenic phase then follows in which methanogenic bacteria convert the fatty acids into biogas.

The biogas is stored in the gas storage tank, while the digested sludge undergoes mechanically thickening on a centrifuge until the content of dry matter reaches approximately thirty percent. Thickened sludge is stored at the disposal site ready for final disposal. Pumps then transfer the centrate to a storage tank where it undergoes deammonification.

Biogas is mixture of approximately sixty-five percent of methane, thirty-four percent of carbon dioxide and one percent of other gases. After digestion, the Biogas passes from the gas storage tank through a column containing activated carbon, which removes impurities such as organic silicon compounds, solvents and sulphide to a generator to produce electricity. The electrical energy produced covers over ninety percent of the treatment plant's energy needs as well as providing all the heat energy required by the treatment processes. Any excess electricity produced goes back into the electrical grid, while flares dispose of any excess biogas.

Tabel 1:

 

Waste Classfication – List of Waste (operation R3/R1)
Non- hazardous biodegradable waste (hygienisation of liquid waste)

 

Waste Classification List of Waste
02 01 01 sludges from washing and cleaning
02 01 03 plant-tissue waste
02 02 03 materials unsuitable for consumption or processing
02 02 04 sludges from on-site effluent treatment
02 03 01 sludges from washing, cleaning, peeling, centrifuging and separation
02 03 04 materials unsuitable for consumption or processing
02 03 05 sludges from on-site effluent treatment
02 04 03 sludges from on-site effluent treatment
02 05 01 materials unsuitable for consumption or processing
02 05 02 sludges from on-site effluent treatment
02 06 01 materials unsuitable for consumption or processing
02 06 03 sludges from on-site effluent treatment
02 07 01 wastes from washing, cleaning and mechanical reduction of raw materials
02 07 02 wastes from spirits distillation
02 07 04 materials unsuitable for consumption or processing
02 07 05 sludges from on-site effluent treatment
03 03 10 fibre rejects, fibre-, filler- and coating-sludges from mechanical separation
03 03 11 sludges from on-site effluent treatment other than those mentioned in 03 03 10
04 02 20 sludges from on-site effluent treatment other than those mentioned in 04 02 19
07 05 14 solid wastes other than those mentioned in 07 05 13
08 04 10 waste adhesives and sealants other than those mentioned in 08 04 09
08 04 12 adhesive and sealant sludges other than those mentioned in 08 04 11
08 04 14

aqueous sludges containing adhesives or sealants other than those mentioned in 08 04 13

16 03 06 organic wastes other than those mentioned in 16 03 05
19 05 03 off-specification compost
19 06 05 liquor from anaerobic treatment of animal and vegetable waste
19 06 06 digestate from anaerobic treatment of animal and vegetable waste
19 08 05 sludges from treatment of urban waste water
19 08 09 grease and oil mixture from oil/water separation containing only edible oil and fats
19 08 12 sludges from biological treatment of industrial waste water other than those mentioned in 19 08 11
19 08 14 sludges from other treatment of industrial waste water other than those mentioned in 19 08 13
19 09 02 sludges from water clarification
19 09 03 sludges from decarbonation
20 01 08 biodegradable kitchen and canteen waste
20 01 25 edible oil and fat
20 02 01 biodegradable waste
20 03 02 waste from markets
20 03 06 waste from sewage cleaning