Conversion of biological sludge and primary float sludge to animal protein supplement

A protein-enrichment process for converting float sludge into a nutritional animal feed supplement and for biologically altering the proportion of fat to protein in said float sludge, comprising the following steps:

• A. admixing a food process wastewater with a supernate, a coagulation agent, compressed air, and a flocculation agent for forming a pressurized liquid mixture;
• B. releasing the pressure on said pressurized liquid mixture, whereby small bubbles of air float protein and fat particles to the surface of said liquid mixture, and skimming said risen particles to form said float sludge;
• C. bubbling air through said float sludge until said float sludge has been digested by microorganisms;
• D. settling the digested float sludge to produce a bottom layer of sludge and a layer of supernate;
• E. recycling said supernate for admixing with said food process wastewater of said Step A;
• F. discharging said digested sludge layer as an enriched float sludge containing large amounts of protein and fat;
• G. admixing said enriched float sludge with a bulking agent to form a bulked mixture;
• H. heating, aerating, and drying said bulked mixture while absorbing a portion of said sludge fat with said bulking agent;
• and
• I. separating the dried and partially defatted sludges from the fat-containing bulking agent to produce a meal having utility as said animal feed supplement.

In a process for disposal of a wastewater from a proteinaceous food preparation plant,

• wherein:
• (a) as a pretreatment, said wastewater is admixed with a coagulation agent, compressed air, and a flocculation agent and is then admitted to a flotation cell at atmospheric pressure, whereby proteins and fats are brought to the liquid surface and are skimmed to produce a float sludge which has a low solids content, contains protein, and is high in sludge fat, and a partially purified wastewater which is aerobically digested in an activated sludge basin to produce an activated biological sludge and a clarified liquor, said activated biological sludge having a solids content of about 3-5% solids by weight after thickening thereof, and
• (b) there is a need for a process for disposal of said sludges and particularly a need for a process capable of converting said sludges into an animal feed supplement of high protein content and adequately low fat content,
• the improvement which comprises:
• A. admixing said float sludge and said activated sludge with a bulking agent to form a bulked mixture, said bulking agent having properties rendering it capable of:
• (1) dispersion of said sludges onto its surfaces, to form sludge coatings thereon, during stirring of said bulked mixture,
• (2) absorbing liquefied fat from said sludge coatings, and
• (3) being separable from said sludge coatings after drying thereof;
• B. stirring, heating, and aerating said bulked mixture while:
• (1) liquefying said fat in said sludge coatings,
• (2) absorbing a portion of said liquefied fat into said bulking agent, and
• (3) drying said mixture to form a dried mixture in which the dried and partially defatted sludges exist as said dried sludge coatings;
• and
• C. separating said dried sludge coatings from said fat-containing bulking agent and recovering said sludge coatings as said meal having utility as said animal feed supplement.

A process for biological oxidation of fat and its conversion to biomass in a float sludge, which is produced by dissolved-air flotation of wastewater from a meat processing plant after admixture of a flotation agent, compressed air, and a coagulation agent and subsequent depressurization of said admixed wastewater, in order to increase:

• (a) the settleability of said float sludge and the consequent concentration of sludge solids and (b) the protein-fat ratio in said float sludge, said process comprising:
• A. providing said sludge with a biological culture;
• B. continuously aerating said cultured sludge for a plurality of days in a sludge enrichment digester having sufficient depth for settlement therewithin;
• C. allowing said aerated sludge to settle when a desired protein-fat ratio is reached;
• and
• D. withdrawing settled sludge, as an enriched float sludge, from the bottom of said digester and supernate from a portion of said digester above said settled sludge.