Slaughterhouse and Meat Processing Wastewater: Flow, Load and Process Parameters in HJ 2004-2010

1. Get flow and water quality right before choosing the process

HJ 2004-2010, Technical specifications for slaughterhouse and meat processing wastewater treatment, was approved by the former Ministry of Environmental Protection on 2010-12-17 and took effect on 2011-03-01. Chapter 4 is unusually concrete about how to fix the pollution load. Wastewater quantity is calculated as Q equals q times S, with the unit wastewater generation per slaughtered animal taken from Tables 1 and 2: for livestock, cattle 1.0 to 1.5 m3 per head, pigs 0.5 to 0.7 m3 per head and sheep 0.2 to 0.5 m3 per head; for poultry, chickens 1.0 to 1.5, ducks 2.0 to 3.0 and geese 2.0 to 3.0 m3 per 100 birds. A standalone meat processing plant should generally not exceed 5.8 m3 per tonne of raw meat, and plants with cutting, rendering or similar operations add 2 m3 per tonne of raw meat. Where the estimate is based on total plant water use, wastewater quantity is taken as 80 to 90 percent of total water use.

Water quality must be based on measured data. Where monitoring data are absent, slaughterhouse wastewater follows Table 3 (CODCr 1500 to 2000, BOD5 750 to 1000, suspended solids 750 to 1000, ammonia nitrogen 50 to 150 and animal and vegetable oils 50 to 200 mg/L, pH 6.5 to 7.5) and meat processing wastewater follows Table 4 (CODCr 800 to 2000, BOD5 500 to 1000, suspended solids 500 to 1000, ammonia nitrogen 25 to 70 and oils 30 to 100 mg/L, pH 6.5 to 7.5). The CODCr upper bounds are the same but the meat processing lower bound is much smaller and ammonia nitrogen is markedly lower, so the two tables must not be mixed when fixing design influent values.

Chapter 5 adds three easily overlooked mandatory requirements: main treatment facilities shall be designed with not fewer than two cells or two parallel trains with standby for main equipment (clause 5.1.5); the process shall include disinfection and deodorisation units (clause 5.1.7); and the plant shall install on line wastewater monitoring equipment under the Measures for the Administration of Automatic Monitoring of Pollution Sources and local rules (clause 5.1.9). Clause 6.1.4 sets the tone: a combined process with biological treatment as the main line and physico chemical treatment as support shall be adopted.

2. Pretreatment: oil and suspended solids must be intercepted first

• Screens (clause 6.3.1.1): coarse and fine screens shall be installed upstream of the equalisation tank and designed for the maximum hourly flow; mechanical screens with automatic cleaning are preferred at large flows with much floating debris; poultry slaughter wastewater carries large amounts of feathers, so dedicated fine screens, hydrosieves or wedge wire screens are mandatory.
• Grit chambers (clause 6.3.1.2): horizontal flow type with a maximum velocity of 0.3 m/s, a minimum of 0.15 m/s and a retention of 30 to 60 seconds; vortex type with a swirl velocity of 0.6 to 0.9 m/s, a surface loading of about 200 m3 per square metre per hour and a retention of 20 to 30 seconds.
• Oil separators (clause 6.3.1.3): placed after the grit chamber and before the equalisation tank; horizontal flow retention of 1.5 to 2.0 hours, and not more than 0.5 hours for inclined plate types; meat processing wastewater with low oil content may omit a separate unit.
• Collection tank (clause 6.3.1.4): effective volume not less than 5 minutes of output from the largest duty pump; lift pumps selected on maximum hourly flow, or 3 to 4 times the average flow where no flow variation curve exists, with not more than 6 starts per hour.
• Equalisation tank (clause 6.3.1.5): where no data exist, size on 10 to 24 hours retention with allowance for emergency storage; submersible mixing power generally 5 to 10 W per cubic metre, or air mixing at 0.6 to 0.9 normal m3 per hour per cubic metre; preferably covered with ventilation and deodorisation; floor slope not less than 2 percent towards the sump.
• Primary sedimentation (clause 6.3.1.6): vertical flow preferred, radial flow permissible above 3000 tonnes per day; vertical flow diameter or side preferably not above 8 m with a width or diameter to depth ratio generally not above 3; centre velocity not above 30 mm/s without a baffle and 100 mm/s with one; retention above 1 hour but preferably not above 3 hours.
• Dissolved air flotation (clause 6.3.1.7): an optional technology for residual dispersed oil, emulsified oil, hair and fine suspended solids; preferred for meat processing wastewater rich in oil and hair, to protect the stability of the downstream anaerobic unit.

3. Biological treatment: two routes for the anaerobic stage

3.1 UASB (clause 6.3.2.1)

Suited to medium to high organic loading with relatively stable flow and quality and low suspended solids. Design by volumetric loading and check by hydraulic retention time, with HRT preferably 16 to 24 hours; ambient or mesophilic operation is preferred, with heating and insulation where water temperature is low. Table 5 gives volumetric loading rates on CODCr by temperature: 2 to 5 kg per cubic metre per day at ambient temperature (15 to 30 degrees C) and 5 to 10 at mesophilic temperature (30 to 35 degrees C). Four further hard parameters apply: height preferably not above 8 m, with a recommended effective sludge bed height of 3.0 to 3.5 m; pH maintained between 6.8 and 7.6, with Ca(OH)2, NaHCO3 or Na2CO3 added as needed to keep pH above 6.8; the inclined wall angle of the settling zone in the three phase separator not less than 45 degrees, with surface loading below 0.75 m3 per square metre per hour without inclined tubes and 1.0 to 1.5 with them, and gap velocity not above 2 m/h; and biogas recovery or safe high level combustion must be provided.

3.2 Hydrolysis acidification (clause 6.3.2.1)

Suited to higher volumetric loading with strongly fluctuating flow and quality. Design is normally by hydraulic retention time with organic volumetric loading as the check: HRT 4 to 10 hours and a CODCr volumetric loading of 4.8 to 12.0 kg per cubic metre per day; the maximum upflow velocity shall be below 2.0 m/h; temperature shall be kept above 15 degrees C, preferably 20 to 30 degrees C; biofilm media may be hung, with media height generally one half to two thirds of the effective tank depth.

3.3 Aerobic treatment: SBR, contact oxidation and MBR

• SBR (clause 6.3.2.2): sludge loading (BOD5 to MLVSS) preferably 0.1 to 0.4 kg per kg per day; total cycle 6 to 12 hours, of which filling 1 to 2 hours, reaction 4 to 8 hours, settling 1 to 2 hours, decanting 0.5 to 1.5 hours and idle 1 to 2 hours; the text specifically identifies ammonia nitrogen and water temperature as the governing design factors, requiring nitrification rate to be calculated from the lowest wastewater temperature together with the ammonia nitrogen effluent limit and the reactor volume to be checked accordingly.
• Contact oxidation: HRT 8 to 12 hours with a media volumetric loading (BOD5) of 1.0 to 1.5 kg per cubic metre per day.
• MBR: submerged hollow fibre or flat sheet membranes are preferred; hollow fibre flux is generally designed at 8 to 15 L per square metre per hour and flat sheet flux at 14 to 20; HRT generally 8 to 16 hours; Table 6 gives submerged MLSS of 8000 to 12000 mg/L with a CODCr to MLVSS loading of 0.10 to 0.30 kg per kg per day, and side stream MLSS of 10000 to 15000 mg/L with a loading of 0.30 to 0.60, both with an excess sludge yield of 0.10 to 0.30 kg per kg.
• Secondary sedimentation: vertical flow surface loading 0.6 to 0.8 m3 per square metre per hour, inclined tube 1.0 to 1.5, retention above 1 hour but preferably not above 3 hours; radial flow may be used above 3000 tonnes per day.

4. Disinfection, sludge and odour: the three closing lines

Clause 6.3.2.3 is one of the few mandatory sentences in this specification: wastewater from slaughterhouses and meat processing plants must be disinfected. Chlorine dioxide or sodium hypochlorite is generally used, with a disinfection contact time of not less than 30 minutes and an effective concentration of not less than 50 mg/L; decolourisation may be combined with disinfection.

Sludge (clause 6.6): dominated by excess biological sludge; the excess sludge quantity is generally designed at 0.3 to 0.5 kg per kg (dry solids to BOD5) with a moisture content of 99.3 to 99.4 percent; gravity thickening is preferred with a thickening time of 16 to 24 hours and a thickened moisture content not above 98 percent; chemical conditioning is required before dewatering, with the dose determined by testing or comparable data; dewatered sludge moisture content shall be below 80 percent; for agricultural use the sludge must comply with GB 4284, and for sanitary landfill or separate disposal the moisture content shall be below 60 percent; dewatered sludge must never be stored in the open.

Odour (clause 6.5): units such as the equalisation tank, influent pump station, anaerobic reactor, sludge storage and sludge dewatering should be designed as enclosed with centralised odour collection and treatment; biofilter towers, bioscrubbers and activated carbon adsorption are preferred; and odour pollutant emission concentrations shall comply with GB 14554.

Finally, the limits of this specification must be stated honestly. Clause 6.4.2 gives only a direction for advanced treatment - biological aerated filter, biological activated carbon, coagulation sedimentation and filtration - and explicitly says that the specific combination and the relevant process parameters shall be determined by testing. Beyond clause 6.1.4, all tank volumes and loadings must be calculated from measured or comparable data; the intervals given in the specification are design ranges, not a substitute for the full design calculation.