Innovative technology for treating waste water from slaughterhouses

The aim of the innovative technology studied in this TKI project is to treat high-strength slaughterhouse waste water in a single step, in other words without any form of pre-treatment.The major advantage is that this converts more organic components in the waste water, both in dissolved and non-dissolved form, into biogas during the anaerobic conversion.

Project objective

This project involves laboratory testing, a bench-scale test and a pilot test with the aim of assessing new anaerobic technology developed in the Netherlands for the treatment of high-strength waste water from a pig slaughterhouse. This waste water contains high levels of undissolved organic matter and high levels of fat, oil and grease (FOG). The aim of the project was to demonstrate the effectiveness and robustness of the wastewater treatment technology. In addition, the study was expected to establish a clearer picture of the parameters that are important for the further optimisation and upscaling of the technology.

Technology

The project focuses on Sparthane™ technology, which was developed specifically for high-strength waste water. The technology consists of an unconventional self-regulating anaerobic SBR or AnSBR (anaerobic sequencing batch reactor). Although the system processes the waste water in batches, what most distinguishes it from conventional anaerobic SBR systems is that it conducts different stages of the treatment process simultaneously in each cycle. This means that reaction times are maximised and that complete degradation is achieved without compromising the total duration of the process.

Challenge

The treatment of wastewater streams with slowly degradable substrates, such as suspended solids and fat, oil and grease (FOG), is a major challenge for the food industry. It is particularly difficult to achieve the complete degradation of the compounds in the waste water, and prevent their accumulation in the reactor. In addition, a variety of undesirable effects – such as foaming events, sludge floating, and high long-chain fatty-acid concentration – can occur during the course of the treatment. These complications make it difficult to treat high-strength slaughterhouse waste water efficiently. Although there are other technologies that can achieve high biodegradation levels, there is as yet no simple, single-stage method for the effective and efficient anaerobic treatment of slaughterhouse waste water. All the tests in this project were conducted with waste water from a pig slaughterhouse where the waste water is treated conventionally in a system consisting of a dissolved air flotation (DAF) unit for pre-treatment, followed by an upflow anaerobic sludge blanket reactor (UASB).

Results

The study successfully tested the new technology, both at a small scale and at a pilot scale. The system functioned stably at a volumetric load of 3 g COD/litre reactor/day, with a removal efficiency for total COD of 75%. The system easily accommodated fluctuations in the load up to values of 6.2 g COD/litre reactor/day. Comparison of the pilot data with data for the conventional DAF-UASB leads to the conclusion that biogas production from the AnSBR system is up to 25% higher. In addition, lower effluent concentrations for N and P were measured with the AnSBR, making further nutrient removal (biological or physical/chemical) and aerobic treatment of the wastewater stream more cost-effective.

Other benefits of the AnSBR system are that disposal of sludge from the pre-treatment stage is no longer necessary. Furthermore, the space requirements for the SBR reactor are much smaller.

Given all the above, the researchers estimate that the operating costs per m3 of waste water, which is 1.33 euros for the DAF+UASB configuration, can be reduced to 0.60 euros for the AnSBR technology.

The only drawback of the AnSBR system compared with conventional systems is that operation on a batch basis may present some challenges or complexities with regard to the operation of the reactor system, even though this is, in principle, self-regulating. In addition, the quality of the sludge produced by technology based on flocculant sludge such as the AnSBR is different from that of a granular sludge bed reactor such as the UASB and has therefore no value for sale as a seed material.

The overall conclusion is that this successful practical trial provides companies from the food sector that have complex and highly contaminated waste water with the prospect of an effective and, above all, cheaper solution for the direct anaerobic treatment of the waste water.