Treatment of typical South African milking parlour wastewater by means of anaerobic sequencing batch reactor technology.

Du Preez, Jeanne (2010-03)

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: Due to the growing demands for fresh and clean water, the investigation into the treatment, reuse and recycling of wastewater from all industries are becoming more of a priority, both globally and in South Africa where as much as 62 % of the total water used per year is used by the agricultural sector. The investigation into the recycling and reuse of wastewater in the agricultural sector (especially the dairy farming industry) is therefore no exception. The water usage in five typical South African milking parlours was estimated in this study and ranged from 15 to 51 L.cow-1.day-1. However, the water used for the cleaning in place (CIP) washing of the milking equipment were rather similar in all five milking parlours and ranged between 4.9 and 6.4 L.cow-1.day-1. The possibility of handling and treating the CIP wastewater separately from the rest of the milking parlour wastewater has been considered in the past by other researchers. Anaerobic digestion, as a means of treating wastewater from the dairy industry, has been employed successfully in both full scale and laboratory scale projects. The wastewater from equipment washing of milking parlours is assumed to have similar characteristic to that generated from dairy factories. The anaerobic sequencing batch reactor (ASBR) system is gaining popularity as a wastewater treatment technology lately due to its simplicity, ease of operation and compact design and is therefore expected to be a suitable and practical solution for dairy farmers in treating milking parlour wastewater from equipment washing. Investigation into anaerobic treatment at lower temperatures than the conventional mesophilic range is also becoming of interest due to lower energy requirements. The aim of this study was to determine whether the ASBR technology could be considered as a suitable technology for treating wastewater from the CIP washing of milking parlour equipment. To support this study, the water usage and CIP effluent generated at typical South African milking parlours were firstly verified. Subsequently, laboratory work entailed: • Assessing the sensitivity of the ASBR process (at mesophilic temperature of 35 °C) to fluctuations in the concentration of the detergents in synthetic CIP milking parlour wastewater; and • Evaluating the performance of the ASBR process at 22.5 and 35 °C when treating real wastewater from the CIP washing of milking equipment. Chemical oxygen demand (COD) removal efficiencies between 89 and 98 % were achieved when the synthetic wastewater (similar to wastewater from the CIP washing of milking equipment with COD concentrations ranging between 12 600 and 13 400 mg.L-1) was treated in an ASBR. The results showed that an increase in the CIP detergent concentration up to four times the concentration normally used in milking parlours did not significantly affect the ASBR performance in terms of methane productivity, methane yield and COD removal efficiencies when OLRs between 0.6 and 5.2 g COD.L-1.day-1 were applied. The results also showed that COD removal efficiencies between 92 and 98 % could be achieved in the ASBR process operated at 35 °C when treating real CIP milking parlour effluent (with COD concentrations ranging between 14 900 and 28 800 mg.L-1) when applying OLRs up to 6.6 g COD.L-1.day-1, without nutrient control. Therefore, the ASBR process is suitable to treat real milking parlour wastewater with OLRs above 6 g COD.L-1.day-1 at mesophilic temperatures. At an operating temperature of 22.5 °C, the ASBR achieved TCOD removal efficiencies between 86 and 98 % when treating real CIP effluent. Despite these high COD removal efficiencies, the reactor failed at an OLR of 2.9 g COD.L-1.day-1. As such, the ASBR process appears to be susceptible to failure (due to overloading) when the OLR is increased too rapidly at this low operating temperature. This is most probably due to the fact that methanogenic bacteria do not acclimatise and operate as well at temperatures below the mesophilic range. However, during a second attempt at 22.5 oC, the ASBR achieved COD removal efficiencies between 89 and 97 % when the OLR was increased less rapidly, up to 3.3 g COD.L-1.day-1. These results show that the ASBR process can indeed treat real milking parlour wastewater at 22.5 °C without nutrient control at OLRs above 3 g COD.L-1.day-1. The COD concentration in the effluent from the ASBRs when the maximum OLRs were applied were always below 1 000 mg.L-1. This is notably lower than the South African legal limit for irrigation of up to 50 m3 of wastewater per day. However, this is significantly higher than the South African legal limit of 75 mg.L-1 for safe disposal into a fresh water body.

AFRIKAANSE OPSOMMING: Die wêreldwye toename in die aanvraag na vars, skoon water het tot gevolg dat die ondersoek in die behandeling, hergebruik en herwinning van afvalwater tans groot aandag geniet. Nie net wêreldwyd nie, maar ook in Suid-Afrika waar tans 62 % van die water wat gebruik word per jaar, aangewend word vir die lanbou sektor. Daarom is die ondersoek na besparing van water in lanbou aktiwiteite (veral melkboerderye) geen uitsondering nie. Die watergebruik tydens melktyd in 5 verskillende melkerye is ondersoek en dit blyk dat die watergebruik in die 5 melkery drasties van mekaar verskil. Dit strek van ‘n minimum van 15 litres per koei per dag tot ‘n maksimum van 51 liters per koei per dag. Die volume water wat gebruik word vir die outomatiese was van die melktoerusting het nie so baie gevarieer nie en het gestrek tussen 4.9 en 6.4 liter per koei per dag. Die moontlikheid om die afvalwater wat gegenereer word tydens die outomatiese was van die melktoerusting apart te hou van die res van die afvalwater, is in die verlede deur ander navorsers oorweeg. Afvalwater van suiwelfabrieke is in die verlede al deur middel van anaerobiese vertering in ‘n groot aantal laboratorium- en volskaalse anaerobiese aanlegte behandel. Daar word aangeneem dat die afvalwater wat gegenereer word tydens die was van melktoerusting min of meer dieselfde samestelling sal hê as die afvalwater van suiwelfabrieke. Die anaerobiese opvolgende lot reaktor (AOLR) word al hoe meer gewild in anaerobiesewaterbehandeling as gevolg van die eenvoudige en maklike werking en kompakte ontwerp. Dit word verwag dat hierdie tegnologie ‘n gepaste en praktiese oplossing sal wees om die afvalwater van die was van melktoerusting te behandel. Die anaerobiese behandeling van afvalwater by temperature laer as die normale mesofiliese temperature word ook al hoe meer gewild as gevolg van minder hitte wat benodig word. Die doel van hierdie studie was om te bepaal of die AOLR tegnologie ‘n gepaste tegnologie is om afvalwater wat gegeneer word tydens die outomatiese was proses van melkery toerusting te behandel. Ter ondersteuning van die doel, is die watergebruik in ‘n paar tipiese, Suid- Afrikaanse melkerye eers bevestig. Daaropvolgend, het die laboratoriumwerk die volgende behels: • The bepaal of die AOLR proses (wat by mesofiliese temperatuur van 35 °C bedryf was) sensitief is vir veranderinge in die konsentrasie van sepe in sintetiese waswater wat na ‘n AOLR gevoer word; en • Om die werking van die AOLR proses te ondersoek wanneer regte afvalwater van melkery by onderskeidelik 22.5 en 35 °C behandel word. Chemiese suurstof behoefte (CSB) verwydering van 89 to 98 % is bereik toe sintetiese afvalwater wat gelykstaande aan afvalwater gegenereer tydens die was van melk toerusting is (met CSB konsentrasies tussen 12 600 en 13 400 mg.L-1) in ‘n AOLR behandel is. Die resultate het getoon dat daar geen aanmerklike verskil in die werking van die AOLR in terme van metaanproduksie, metaanopbrengs en CSB verwyderingseffektiwiteit was met a toename tot en met so hoog as vier maal die normale seepkonsentrasie in die afvalwater was toe organiese ladingstempo’s (OLTs) tussen 0.6 en 5.2 g CSB.L-1.dag-1 aangewend was nie. Die resultate het ook getoon dat die CSB van regte afvalwater van melkerye (met CSB konsentrasies tussen 14 900 en 28 800 mg.L-1) met 92 tot 98 % verminder kan word wanneer dit in ‘n AOLR (wat by 35 °C bestuur word) en OLTs tot so hoog as 6.6 g CSB.L-1.dag-1 aangewend word, sonder dat die nutrientinhoud in die afvalwater beheer was. Hierdie AOLR proses wat is dus gepas om afvalwater van melkery te behandel met OLTs bo 6 CSB.L-1.dag-1 by mesofiliese temperature. Die AOLR wat by ‘n temperatuur van 22.5 °C bedryf was, het CSB verwydering tussen 86 en 98 % behaal. Ondanks die hoë CSB verwydering het die reaktor misluk by ‘n maksimum OLT van 2.9 g CSB.L-1.dag-1. Dit het getoon dat die AOLR proses meer geneig is om vatbaar te wees vir mislukking (as gevolg van ‘n oorlading) wanneer die OLT te vinnig verhoog word by laer temperature. Dit is moontlik as gevolg daarvan dat die metanogeniese bakterieë nie so goed aanpas en werk by temperature laer as mesofiliese temperature nie. Nietemin, tydens ‘n tweede probeerslag by 22.5 °C, het die AOLR CSB verwydering tussen 89 en 97 % behaal tydens ‘n stadiger toename in die OLT tot en met 3.3 g CSB.L-1.dag-1. Hierdie resultate dui aan dat die AOLR proses wat by ‘n temperatuur van 22.5 °C bedryf word ook gepas is om afvalwater van melkerye te behandel, sonder nutrient beheer by OLTs hoër as 3 g CSB.L-1.dag-1. Die CSB konsentrasies in die afvloeisel van die AOLR’e in die studie tydens die aanwending van die hoogste OLTs, was altyd laer as 1 000 mg.L-1. Dit is merkbaar laer as die limiet vir besproeiing van tot en met 50 m3 per dag in Suid-Afrika. Maar, dit was nogtans regdeur hoër as die limiet van 75 mg.L-1 vir veilige storting in ‘n varswaterbron.

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