This invention pertains to an organic slurry treatment process, which may be used to recover organic matter and nutrients from animal manure slurry, for instance pig slurry, as well as any industrial or agricultural waste with high organic matter and nutrient concentrations.
Over the last twenty years, and especially in the last five years due to increased regulatory and public pressures placed upon confined animal feedlots and other high-strength waste generators, extensive research has been done in the US, Europe and Japan to develop various processes to treat high-organic waste streams such as pig slurry.
Important patent ed contributions for the treatment animal waste and other high-strength organic waste processes are disclosed in: U.S. Pat. No. 6,346,240 (Moore, Jr.), U.S. Pat. No. 6,221,650 (Rehberger), U.S. Pat. No. 6,007,719 (yoo, et al.), U.S. Pat. No. 5,885,461 (Terault, et al.), U.S. Pat. No. 6,077,548 (Lasseur, et al.), U.S. Pat. No. 6,139,744 (Spears, et al.), U.S. Pat. No. 6,207,507 (White), U.S. Pat. No. 5,013,441 (Goronszy), U.S. Pat. No. 5,277,814 (Winter, et al.), U.S. Pat. No. 6,054,044 (Hoffland, et al.), and U.S. Pat. No. 6,083,386 (Lloyd).
There have been several patents granted for processes that utilize conventional and/or patented technologies and/or processes in novel applications, arrangements and/or combinations. For example, within the field of animal waste treatments the following patents cover some of the treatment processes utilizing conventional technologies: electrochemical treatment (U.S. Pat. No. 6,083,377 (Lin et al.)), ozonation (U.S. Pat. No. 6,117,324 (Greene, et al.)), ozone disinfection (U.S. Pat. No. 6,056,885 (Wasinger)), anaerobic fermentation (U.S. Pat. No. 5,282,879 (Baccarani)), psychrophilic anaerobic digestion (U.S. Pat. No. 5,863,434 (Masse, et al.)), microbiological treatment (U.S. Pat. No. 5,707,856 (Higa)), aerobic systems (U.S. Pat. No. 6,136,185 (Sheaffer)), constructed wetlands (U.S. Pat. No. 6,159,371, (Dufay)), inter alia. Other prior art references are listed under xe2x80x98Referencesxe2x80x99 below.
The organic slurry treatment process according to the present invention combines patented systems and technologies in a way that creates a novel process to treat organic slurries. The synergies created by the specific sequencing of treatment systems in this process maximize treatment capacity and recovery of organic matter and nutrients for use as organo-mineral fertilizer.
Accordingly, the present invention provides a process for treating an organic slurry comprising a mixture of solids suspended in a liquid, colloidal solids and dissolved pollutants such as nitrogen, phosphorus and organic matter, the process comprising:
flocculating a slurry stream with anionic polymer or a coagulant, or both, to aggregate suspended and colloidal solids into a floc, to form a flocculated stream;
removing flocs from the flocculated stream to form a deflocced stream;
feeding the deflocced stream into a high biomass concentration suspended growth system to remove biologically at least a portion of the organic and inorganic nitrogen, and remove by biological luxury uptake at least a portion of the phosphorus, wherein the system comprises:
a multi-stage sequence of an anaerobic zone, an anoxic zone, and an aerobic zone, each zone separated with baffles, operating in a biomass recycle pattern from the anoxic zone to the anaerobic zone, and from the aerobic zone to the anoxic zone, with biomass wastage from the aerobic zone; and
microfiltration membranes to filter liquid out of the aerobic zone to form a low-turbidity permeate.
The approach of the process according to the present invention to organic slurry and manure treatment differs from that of conventional processes, which usually rely on anaerobic digestion. The present organic slurry treatment process is based on effectively separating solids from liquids in the waste slurry stream. Solids are dried and pelletized, and liquid is subjected to physical, chemical, and biological treatment. The treatment of the liquid fraction removes suspended solids, colloidal solids, nitrogen, phosphorus and dissolved organic matter.
Advantageously, the process according to the present invention can eliminate the need for anaerobic digestion, waste lagoons and/or land application when treating animal manure slurries.
Several treatment steps are required to fully treat organic slurries while recovering their organic and nutrient value. First, for treating organic slurries that have high solids content, once slurry waste has been received stored and mixed, solids are separated, preferably using a centrifugal decanter. Solids capture efficiency can be enhanced by cationic polymer addition. In this step the waste stream is divided into a solids and a liquid fraction. The solids fraction, or cake, retains a significant portion of the total amount of solids, organic matter and phosphorus. The liquid fraction or centrate still maintains some particulate and all colloidal and dissolved pollutants.
The solids fraction is dried and pelletized using a direct or indirect continuous heat-drying system and a paddle mixer. This process destroys pathogens and produces hard, uniformly sized and stable pellets for use as organo-mineral fertilizer. On-site drying/pelletizing offers the following advantages: reduces transportation cost, enables heat recovery from the drying process to be used to enhance biological centrate treatment and provides nitrogen-rich condensate. Condensate contains ammonium nitrogen and easily degradable volatile organic matter. The nitrogen present in the condensate in the form of ammonium is recovered using a chemical/physical system consisting of an air stripping packed media tower followed by an acid scrubbing packed media tower. The nitrogen recovered in the form of a concentrated ammonium sulphate solution is used to fortify the nutrient value of the pellets. After ammonium removal, condensate with high dissolved organic matter content is used as a carbon source for denitrification in the biological removal system, as described below.
Alternatively, for treating organic slurries having a low solids content, for example wastewater, the slurry need not be separated initially to remove solids but can be treated directly according to the following process steps.
Suspended and colloidal solids remaining in the centrate, or in low solids slurry such as wastewater, are removed, preferably using dissolved air flotation thickening (DAFT), preceded by flocculation. This process is enhanced with the addition of anionic polymer and coagulant to the flocculation unit.
DAFT effluent is preferably heated to mesophilic temperature, preferably using an indirect tube and shell or plate heat exchanger. Heat for this step is available in return condenser cooling water, which is used to condensate water vapour removed from the solids cake in the drying/pelletizing system. Alternatively, heat can be made available using a water heater operated with liquid or gasfuel. Higher DAFT effluent temperature enhances bacterial metabolism, which increases biological reaction rates in the treatment steps following downstream.
Unless the deflocced stream is readily biodegradable, dissolved complex organic matter and volatile solids in the deflocced stream, for example in heated DAFT effluent, are simplified into short-chain volatile fatty acids (VFA) in a pre-acidification anaerobic fluidized bed reactor (AFBR). AFBR effluent feeds the biological nutrient removal (BNR) system. A high VFA to phosphorus ratio in the BNR feed is required for efficient biological phosphorus removal.
Acidified effluent from the AFBR, or the deflocced stream if readily biodegradable, and preferably also stripped condensate from the ammonium recovery process, are fed to the BNR, which is designed to biologically remove phosphorus and nitrogen, while consuming organic matter simplified to VFA in the AFBR as carbon source for these processes. Carbon requirements for denitrification and phosphorus removal are supplied by VFA available in acidified effluent supplemented by volatile organic matter present in the stripped condensate. BNR treatment rate and efficiency in this process are maximized using submerged microfiltration membranes along with a multi-stage suspended growth biological nutrient removal system. The synergies brought about by this membrane bioreactor/biological nutrient removal (MBR/BNR) combination enable the system to remove efficiently very high dissolved organic matter, nitrogen and phosphorus loads. Additionally, this combination provides high solids retention time, which introduces process stability, reduces biomass production and enables slow-growing organisms, such as nitrifiers, to establish a healthy population. Heavy metals present in the waste stream are also significantly reduced in this system.
The MBR/BNR system comprises a multi-stage Modified Bardenpho configuration with a sequence of at least anaerobic, anoxic and aerobic suspended growth zones, and preferably consists of a five-stage Modified Bardenpho configuration with a sequence of anaerobic, anoxic, aerobic, anoxic and aerobic suspended growth zones. The pattern of biomass recirculation between zones is typical of a conventional University of Cape Town (UCT) process flow. Effective separation of liquid and biomass achieved with microfiltration membranes submerged in the final aerobic zone allows the system to operate with extremely high biomass concentrations and long solids retention times. The liquid passing through the membrane or permeate has no suspended solids, extremely low phosphorus, nitrogen and dissolved organic matter. Microfiltration removes a significant portion of pathogen indicator organisms and produces an effluent with low turbidity. If necessary, the permeate is disinfected using low dosages of ultraviolet radiation prior to reuse as plant service water and discharge.
The combination of the five-stage suspended growth sequence, the biomass recycle pattern, and the microfiltration membranes producing permeate from aerobic zone 2 creates a synergistic effect that enables biological removal of high loads of nitrogen, phosphorus and dissolved organic matter contained in any liquid waste with high concentrations thereof.