Assessment of an integrated and sustainable multi-stage system for the treatment of poultry slaughterhouse wastewater

Abstract

The poultry industry has become a major contributor to the South African agricultural industry due to the growing affordable poultry product demand compared to other animal protein. However, the water requirements for bird slaughtering and the product preparation processes including cleaning, are extensive. Operating abattoirs is governed by the South African Meat Safety Act no. 40 of 2000 and the Abattoir Hygiene Act no. 121 of 1992, both for high and low producers (quantified by the number of birds slaughtered per day). These acts clearly dictate that the provision of clean and safe consumer products is of importance. To achieve this, bird processing requires at least >15 litres of high pressured, filtered and chlorinated water per bird. A typical high-volume abattoir that slaughters over ten thousand birds per day can produce more than one hundred and fifty thousand litres of poultry slaughterhouse wastewater (PSW) that contains a high concentration of organics, nutrients, solids, fat, oil and grease (FOG) and pathogenic microorganisms. The PSW also contains blood, faecal matter, and traces of urine, skin trimmings, feathers and cleaning products. If such untreated PSW is released to the environment, it will be detrimental to the environment, and can cause challenges for municipal sewer systems. For developing countries, the harmful impact includes eutrophication due to nutrient release, stimulating algae growth, and can cause deoxygenation of receiving surface water as a result of organic loading. The Greendrop report publicised South Africa’s (SA’s) water challenges in a report that announced inoperative treatment plants, water lost through poor infrastructure and the release of untreated wastewater into river streams. Thus, highlighting the country’s inability to cope with the additional wastewater treatment requirements. To counter these challenges, there are numerous treatment technologies used for the treatment of PSW. The introduction of High-Rate Anaerobic Digesters (HRADs) has not only shown significant contaminant reduction but has displayed an economical benefit of biogas production. These systems, i.e. anaerobic digesters, have been touted as better than aerobic digesters which requires a large volume of dissolved oxygen thus making it an expensive treatment method. Therefore, this study explored the use of anaerobic digesters for the treatment of high-strength, lipid rich PSW using a down-flow expanded granular bed reactor (DEGBR) due to its anaerobic functionality, cost efficiency, high organic removal rate, ability to produce effluent that has minimal suspended solids, an additional recycle stream, which expands the sludge bed, and reduce clogging. Additionally, due to the established limitations in some anaerobic digester (AD) reactor performance studies, this research included a pre-treatment unit with delipidating abilities, i.e. Fat, Oils and grease (FOG) hydrolysis. Moreover, a membrane bioreactor (MBR) as a tertiary unit for treated water polishing. Over a period of 112 weeks, a pre-treatment, DEGBR and MBR integrated system was operated on a lab-scale. A qualitative analysis was conducted, focusing on the system’s FOG, Total Suspended Solids (TSS) and Chemical Oxygen Demand (COD) removal abilities from the PSW. The eco-dosed pre-treatment had a positive effect on the removal and/reduction for FOG, TSS and COD; albeit, FOG removal exceeded an average of 80%. This had a positive effect of DEGBR performance, which was continuously operated at an organic loading rate (OLR) range of ~18 - ~45 g COD/L.h, achieving a COD, TSS and FOG removal of 87, 93, and 90%, respectively. Furthermore, the system’s overall average removal, i.e. as an integrated pre-treat-DEGBR-MBR system, achieved >99% COD, TSS and FOG removal as an intended outcome for the treatment of PSW; thus, meeting and exceeding set limits for such effluent discharge for South Africa, and in particular, the City of Cape Town’s standards whereby the PSW was sampled.